By Julia Rosen
Ms. Rosen is a journalist with a Ph.D. in geology. Her
research involved studying ice cores from Greenland and Antarctica to
understand past climate changes.
The science of climate change is more solid and widely
agreed upon than you might think. But the scope of the topic, as well as
rampant disinformation, can make it hard to separate fact from fiction. Here,
we’ve done our best to present you with not only the most accurate scientific
information, but also an explanation of how we know it.
How do we know climate change is really happening?
Climate change is often cast as a prediction made by
complicated computer models. But the scientific basis for climate change is
much broader, and models are actually only one part of it (and, for what it’s
worth, they’re surprisingly accurate).
For more than a century, scientists have understood the
basic physics behind why greenhouse gases like carbon dioxide cause warming. These
gases make up just a small fraction of the atmosphere but exert outsized
control on Earth’s climate by trapping some of the planet’s heat before it
escapes into space. This greenhouse effect is important: It’s why a planet so
far from the sun has liquid water and life!
However, during the Industrial Revolution, people started
burning coal and other fossil fuels to power factories, smelters and steam
engines, which added more greenhouse gases to the atmosphere. Ever since, human
activities have been heating the planet.
We know this is true thanks to an overwhelming body of
evidence that begins with temperature measurements taken at weather stations
and on ships starting in the mid-1800s. Later, scientists began tracking
surface temperatures with satellites and looking for clues about climate change
in geologic records. Together, these data all tell the same story: Earth is
getting hotter.
Average global temperatures have increased by 2.2 degrees
Fahrenheit, or 1.2 degrees Celsius, since 1880, with the greatest changes
happening in the late 20th century. Land areas have warmed more than the sea
surface and the Arctic has warmed the most — by more than 4 degrees Fahrenheit
just since the 1960s. Temperature extremes have also shifted. In the United
States, daily record highs now outnumber record lows two-to-one.
This warming is unprecedented in recent geologic history. A
famous illustration, first published in 1998 and often called the hockey-stick
graph, shows how temperatures remained fairly flat for centuries (the shaft of
the stick) before turning sharply upward (the blade). It’s based on data from
tree rings, ice cores and other natural indicators. And the basic picture,
which has withstood decades of scrutiny from climate scientists and contrarians
alike, shows that Earth is hotter today than it’s been in at least 1,000 years,
and probably much longer.
In fact, surface temperatures actually mask the true scale
of climate change, because the ocean has absorbed 90 percent of the heat
trapped by greenhouse gases. Measurements collected over the last six decades
by oceanographic expeditions and networks of floating instruments show that
every layer of the ocean is warming up. According to one study, the ocean has
absorbed as much heat between 1997 and 2015 as it did in the previous 130
years.
We also know that climate change is happening because we see
the effects everywhere. Ice sheets and glaciers are shrinking while sea levels
are rising. Arctic sea ice is disappearing. In the spring, snow melts sooner
and plants flower earlier. Animals are moving to higher elevations and
latitudes to find cooler conditions. And droughts, floods and wildfires have
all gotten more extreme. Models predicted many of these changes, but
observations show they are now coming to pass.
How much agreement is there among scientists about climate
change?
There’s no denying that scientists love a good,
old-fashioned argument. But when it comes to climate change, there is virtually
no debate: Numerous studies have found that more than 90 percent of scientists
who study Earth’s climate agree that the planet is warming and that humans are
the primary cause. Most major scientific bodies, from NASA to the World
Meteorological Organization, endorse this view. That’s an astounding level of
consensus given the contrarian, competitive nature of the scientific
enterprise, where questions like what killed the dinosaurs remain bitterly
contested.
Scientific agreement about climate change started to emerge
in the late 1980s, when the influence of human-caused warming began to rise
above natural climate variability. By 1991, two-thirds of earth and atmospheric
scientists surveyed for an early consensus study said that they accepted the
idea of anthropogenic global warming. And by 1995, the Intergovernmental Panel
on Climate Change, a famously conservative body that periodically takes stock
of the state of scientific knowledge, concluded that “the balance of evidence
suggests that there is a discernible human influence on global climate.”
Currently, more than 97 percent of publishing climate scientists agree on the
existence and cause of climate change (as does nearly 60 percent of the general
population of the United States).
So where did we get the idea that there’s still debate about
climate change? A lot of it came from coordinated messaging campaigns by
companies and politicians that opposed climate action. Many pushed the
narrative that scientists still hadn’t made up their minds about climate
change, even though that was misleading. Frank Luntz, a Republican consultant,
explained the rationale in an infamous 2002 memo to conservative lawmakers:
“Should the public come to believe that the scientific issues are settled,
their views about global warming will change accordingly,” he wrote.
Questioning consensus remains a common talking point today, and the 97 percent
figure has become something of a lightning rod.
To bolster the falsehood of lingering scientific doubt, some
people have pointed to things like the Global Warming Petition Project, which
urged the United States government to reject the Kyoto Protocol of 1997, an
early international climate agreement. The petition proclaimed that climate
change wasn’t happening, and even if it were, it wouldn’t be bad for humanity.
Since 1998, more than 30,000 people with science degrees have signed it.
However, nearly 90 percent of them studied something other than Earth,
atmospheric or environmental science, and the signatories included just 39
climatologists. Most were engineers, doctors, and others whose training had
little to do with the physics of the climate system.
A few well-known researchers remain opposed to the
scientific consensus. Some, like Willie Soon, a researcher affiliated with the
Harvard-Smithsonian Center for Astrophysics, have ties to the fossil fuel
industry. Others do not, but their assertions have not held up under the weight
of evidence. At least one prominent skeptic, the physicist Richard Muller,
changed his mind after reassessing historical temperature data as part of the
Berkeley Earth project. His team’s findings essentially confirmed the results
he had set out to investigate, and he came away firmly convinced that human
activities were warming the planet. “Call me a converted skeptic,” he wrote in
an Op-Ed for the Times in 2012.
Mr. Luntz, the Republican pollster, has also reversed his
position on climate change and now advises politicians on how to motivate
climate action.
A final note on uncertainty: Denialists often use it as
evidence that climate science isn’t settled. However, in science, uncertainty
doesn’t imply a lack of knowledge. Rather, it’s a measure of how well something
is known. In the case of climate change, scientists have found a range of
possible future changes in temperature, precipitation and other important
variables — which will depend largely on how quickly we reduce emissions. But
uncertainty does not undermine their confidence that climate change is real and
that people are causing it.
Do we really only have 150 years of climate data? How is
that enough to tell us about centuries of change?
Earth’s climate is inherently variable. Some years are hot
and others are cold, some decades bring more hurricanes than others, some
ancient droughts spanned the better part of centuries. Glacial cycles operate
over many millenniums. So how can scientists look at data collected over a
relatively short period of time and conclude that humans are warming the
planet? The answer is that the instrumental temperature data that we have tells
us a lot, but it’s not all we have to go on.
Historical records stretch back to the 1880s (and often
before), when people began to regularly measure temperatures at weather
stations and on ships as they traversed the world’s oceans. These data show a
clear warming trend during the 20th century.
Some have questioned whether these records could be skewed,
for instance, by the fact that a disproportionate number of weather stations
are near cities, which tend to be hotter than surrounding areas as a result of
the so-called urban heat island effect. However, researchers regularly correct
for these potential biases when reconstructing global temperatures. In
addition, warming is corroborated by independent data like satellite observations,
which cover the whole planet, and other ways of measuring temperature changes.
Much has also been made of the small dips and pauses that
punctuate the rising temperature trend of the last 150 years. But these are
just the result of natural climate variability or other human activities that
temporarily counteract greenhouse warming. For instance, in the mid-1900s,
internal climate dynamics and light-blocking pollution from coal-fired power
plants halted global warming for a few decades. (Eventually, rising greenhouse
gases and pollution-control laws caused the planet to start heating up again.)
Likewise, the so-called warming hiatus of the 2000s was partly a result of
natural climate variability that allowed more heat to enter the ocean rather
than warm the atmosphere. The years since have been the hottest on record.
Still, could the entire 20th century just be one big natural
climate wiggle? To address that question, we can look at other kinds of data
that give a longer perspective. Researchers have used geologic records like
tree rings, ice cores, corals and sediments that preserve information about
prehistoric climates to extend the climate record. The resulting picture of
global temperature change is basically flat for centuries, then turns sharply upward
over the last 150 years. It has been a target of climate denialists for
decades. However, study after study has confirmed the results, which show that
the planet hasn’t been this hot in at least 1,000 years, and probably longer.
How do we know climate change is caused by humans?
Scientists have studied past climate changes to understand
the factors that can cause the planet to warm or cool. The big ones are changes
in solar energy, ocean circulation, volcanic activity and the amount of
greenhouse gases in the atmosphere. And they have each played a role at times.
For example, 300 years ago, a combination of reduced solar
output and increased volcanic activity cooled parts of the planet enough that
Londoners regularly ice skated on the Thames. About 12,000 years ago, major
changes in Atlantic circulation plunged the Northern Hemisphere into a frigid
state. And 56 million years ago, a giant burst of greenhouse gases, from
volcanic activity or vast deposits of methane (or both), abruptly warmed the
planet by at least 9 degrees Fahrenheit, scrambling the climate, choking the
oceans and triggering mass extinctions.
In trying to determine the cause of current climate changes,
scientists have looked at all of these factors. The first three have varied a
bit over the last few centuries and they have quite likely had modest effects
on climate, particularly before 1950. But they cannot account for the planet’s
rapidly rising temperature, especially in the second half of the 20th century,
when solar output actually declined and volcanic eruptions exerted a cooling
effect.
That warming is best explained by rising greenhouse gas
concentrations. Greenhouse gases have a powerful effect on climate (see the
next question for why). And since the Industrial Revolution, humans have been
adding more of them to the atmosphere, primarily by extracting and burning
fossil fuels like coal, oil and gas, which releases carbon dioxide.
Bubbles of ancient air trapped in ice show that, before
about 1750, the concentration of carbon dioxide in the atmosphere was roughly
280 parts per million. It began to rise slowly and crossed the 300 p.p.m.
threshold around 1900. CO2 levels then accelerated as cars and electricity
became big parts of modern life, recently topping 420 p.p.m. The concentration
of methane, the second most important greenhouse gas, has more than doubled.
We’re now emitting carbon much faster than it was released 56 million years
ago.
These rapid increases in greenhouse gases have caused the
climate to warm abruptly. In fact, climate models suggest that greenhouse
warming can explain virtually all of the temperature change since 1950.
According to the most recent report by the Intergovernmental Panel on Climate
Change, which assesses published scientific literature, natural drivers and
internal climate variability can only explain a small fraction of late-20th
century warming.
Another study put it this way: The odds of current warming
occurring without anthropogenic greenhouse gas emissions are less than 1 in
100,000.
But greenhouse gases aren’t the only climate-altering
compounds people put into the air. Burning fossil fuels also produces
particulate pollution that reflects sunlight and cools the planet. Scientists
estimate that this pollution has masked up to half of the greenhouse warming we
would have otherwise experienced.
Since greenhouse gases occur naturally, how do we know
they’re causing Earth’s temperature to rise?
Greenhouse gases like water vapor and carbon dioxide serve
an important role in the climate. Without them, Earth would be far too cold to
maintain liquid water and humans would not exist!
Here’s how it works: the planet’s temperature is basically a
function of the energy the Earth absorbs from the sun (which heats it up) and
the energy Earth emits to space as infrared radiation (which cools it down).
Because of their molecular structure, greenhouse gases temporarily absorb some
of that outgoing infrared radiation and then re-emit it in all directions,
sending some of that energy back toward the surface and heating the planet.
Scientists have understood this process since the 1850s.
Greenhouse gas concentrations have varied naturally in the
past. Over millions of years, atmospheric CO2 levels have changed depending on
how much of the gas volcanoes belched into the air and how much got removed
through geologic processes. On time scales of hundreds to thousands of years,
concentrations have changed as carbon has cycled between the ocean, soil and
air.
Today, however, we are the ones causing CO2 levels to
increase at an unprecedented pace by taking ancient carbon from geologic
deposits of fossil fuels and putting it into the atmosphere when we burn them.
Since 1750, carbon dioxide concentrations have increased by almost 50 percent.
Methane and nitrous oxide, other important anthropogenic greenhouse gases that
are released mainly by agricultural activities, have also spiked over the last
250 years.
We know based on the physics described above that this
should cause the climate to warm. We also see certain telltale “fingerprints”
of greenhouse warming. For example, nights are warming even faster than days
because greenhouse gases don’t go away when the sun sets. And upper layers of
the atmosphere have actually cooled, because more energy is being trapped by
greenhouse gases in the lower atmosphere.
We also know that we are the cause of rising greenhouse gas
concentrations — and not just because we can measure the CO2 coming out of
tailpipes and smokestacks. We can see it in the chemical signature of the
carbon in CO2.
Carbon comes in three different masses: 12, 13 and 14.
Things made of organic matter (including fossil fuels) tend to have relatively
less carbon-13. Volcanoes tend to produce CO2 with relatively more carbon-13.
And over the last century, the carbon in atmospheric CO2 has gotten lighter,
pointing to an organic source.
We can tell it’s old organic matter by looking for
carbon-14, which is radioactive and decays over time. Fossil fuels are too
ancient to have any carbon-14 left in them, so if they were behind rising CO2
levels, you would expect the amount of carbon-14 in the atmosphere to drop,
which is exactly what the data show.
It’s important to note that water vapor is the most abundant
greenhouse gas in the atmosphere. However, it does not cause warming; instead
it responds to it. That’s because warmer air holds more moisture, which creates
a snowball effect in which human-caused warming allows the atmosphere to hold
more water vapor and further amplifies climate change. This so-called feedback
cycle has doubled the warming caused by anthropogenic greenhouse gas emissions.
Why should we be worried that the planet has warmed 2°F
since the 1800s?
A common source of confusion when it comes to climate change
is the difference between weather and climate. Weather is the constantly
changing set of meteorological conditions that we experience when we step
outside, whereas climate is the long-term average of those conditions, usually
calculated over a 30-year period. Or, as some say: Weather is your mood and
climate is your personality.
So while 2 degrees Fahrenheit doesn’t represent a big change
in the weather, it’s a huge change in climate. As we’ve already seen, it’s
enough to melt ice and raise sea levels, to shift rainfall patterns around the
world and to reorganize ecosystems, sending animals scurrying toward cooler
habitats and killing trees by the millions.
It’s also important to remember that two degrees represents
the global average, and many parts of the world have already warmed by more
than that. For example, land areas have warmed about twice as much as the sea
surface. And the Arctic has warmed by about 5 degrees. That’s because the loss
of snow and ice at high latitudes allows the ground to absorb more energy,
causing additional heating on top of greenhouse warming.
Relatively small long-term changes in climate averages also
shift extremes in significant ways. For instance, heat waves have always
happened, but they have shattered records in recent years. In June of 2020, a
town in Siberia registered temperatures of 100 degrees. And in Australia,
meteorologists have added a new color to their weather maps to show areas where
temperatures exceed 125 degrees. Rising sea levels have also increased the risk
of flooding because of storm surges and high tides. These are the foreshocks of
climate change.
And we are in for more changes in the future — up to 9
degrees Fahrenheit of average global warming by the end of the century, in the
worst-case scenario. For reference, the difference in global average
temperatures between now and the peak of the last ice age, when ice sheets
covered large parts of North America and Europe, is about 11 degrees
Fahrenheit.
Under the Paris Climate Agreement, which President Biden
recently rejoined, countries have agreed to try to limit total warming to
between 1.5 and 2 degrees Celsius, or 2.7 and 3.6 degrees Fahrenheit, since
preindustrial times. And even this narrow range has huge implications.
According to scientific studies, the difference between 2.7 and 3.6 degrees
Fahrenheit will very likely mean the difference between coral reefs hanging on
or going extinct, and between summer sea ice persisting in the Arctic or
disappearing completely. It will also determine how many millions of people
suffer from water scarcity and crop failures, and how many are driven from
their homes by rising seas. In other words, one degree Fahrenheit makes a world
of difference.
Is climate change a part of the planet’s natural warming and
cooling cycles?
Earth’s climate has always changed. Hundreds of millions of
years ago, the entire planet froze. Fifty million years ago, alligators lived
in what we now call the Arctic. And for the last 2.6 million years, the planet
has cycled between ice ages when the planet was up to 11 degrees cooler and ice
sheets covered much of North America and Europe, and milder interglacial
periods like the one we’re in now.
Climate denialists often point to these natural climate
changes as a way to cast doubt on the idea that humans are causing climate to
change today. However, that argument rests on a logical fallacy. It’s like
“seeing a murdered body and concluding that people have died of natural causes
in the past, so the murder victim must also have died of natural causes,” a
team of social scientists wrote in The Debunking Handbook, which explains the
misinformation strategies behind many climate myths.
Indeed, we know that different mechanisms caused the climate
to change in the past. Glacial cycles, for example, were triggered by periodic
variations in Earth’s orbit, which take place over tens of thousands of years
and change how solar energy gets distributed around the globe and across the
seasons.
These orbital variations don’t affect the planet’s
temperature much on their own. But they set off a cascade of other changes in
the climate system; for instance, growing or melting vast Northern Hemisphere
ice sheets and altering ocean circulation. These changes, in turn, affect
climate by altering the amount of snow and ice, which reflect sunlight, and by
changing greenhouse gas concentrations. This is actually part of how we know
that greenhouse gases have the ability to significantly affect Earth’s
temperature.
For at least the last 800,000 years, atmospheric CO2
concentrations oscillated between about 180 parts per million during ice ages
and about 280 p.p.m. during warmer periods, as carbon moved between oceans,
forests, soils and the atmosphere. These changes occurred in lock step with
global temperatures, and are a major reason the entire planet warmed and cooled
during glacial cycles, not just the frozen poles.
Today, however, CO2 levels have soared to 420 p.p.m. — the
highest they’ve been in at least three million years. The concentration of CO2
is also increasing about 100 times faster than it did at the end of the last
ice age. This suggests something else is going on, and we know what it is: Since
the Industrial Revolution, humans have been burning fossil fuels and releasing
greenhouse gases that are heating the planet now (see Question 5 for more
details on how we know this, and Questions 4 and 8 for how we know that other
natural forces aren’t to blame).
Over the next century or two, societies and ecosystems will
experience the consequences of this climate change. But our emissions will have
even more lasting geologic impacts: According to some studies, greenhouse gas
levels may have already warmed the planet enough to delay the onset of the next
glacial cycle for at least an additional 50,000 years.
How do we know global warming is not because of the sun or
volcanoes?
The sun is the ultimate source of energy in Earth’s climate
system, so it’s a natural candidate for causing climate change. And solar
activity has certainly changed over time. We know from satellite measurements
and other astronomical observations that the sun’s output changes on 11-year
cycles. Geologic records and sunspot numbers, which astronomers have tracked
for centuries, also show long-term variations in the sun’s activity, including
some exceptionally quiet periods in the late 1600s and early 1800s.
We know that, from 1900 until the 1950s, solar irradiance
increased. And studies suggest that this had a modest effect on early 20th
century climate, explaining up to 10 percent of the warming that’s occurred
since the late 1800s. However, in the second half of the century, when the most
warming occurred, solar activity actually declined. This disparity is one of
the main reasons we know that the sun is not the driving force behind climate
change.
Another reason we know that solar activity hasn’t caused
recent warming is that, if it had, all the layers of the atmosphere should be
heating up. Instead, data show that the upper atmosphere has actually cooled in
recent decades — a hallmark of greenhouse warming.
So how about volcanoes? Eruptions cool the planet by
injecting ash and aerosol particles into the atmosphere that reflect sunlight.
We’ve observed this effect in the years following large eruptions. There are
also some notable historical examples, like when Iceland’s Laki volcano erupted
in 1783, causing widespread crop failures in Europe and beyond, and the “year
without a summer,” which followed the 1815 eruption of Mount Tambora in
Indonesia.
Since volcanoes mainly act as climate coolers, they can’t
really explain recent warming. However, scientists say that they may also have
contributed slightly to rising temperatures in the early 20th century. That’s
because there were several large eruptions in the late 1800s that cooled the
planet, followed by a few decades with no major volcanic events when warming
caught up. During the second half of the 20th century, though, several big
eruptions occurred as the planet was heating up fast. If anything, they
temporarily masked some amount of human-caused warming.
The second way volcanoes can impact climate is by emitting
carbon dioxide. This is important on time scales of millions of years — it’s
what keeps the planet habitable (see Question 5 for more on the greenhouse
effect). But by comparison to modern anthropogenic emissions, even big
eruptions like Krakatoa and Mount St. Helens are just a drop in the bucket.
After all, they last only a few hours or days, while we burn fossil fuels 24-7.
Studies suggest that, today, volcanoes account for 1 to 2 percent of total CO2
emissions.
How can winters and certain places be getting colder if the
planet is warming?
When a big snowstorm hits the United States, climate
denialists can try to cite it as proof that climate change isn’t happening. In
2015, Senator James Inhofe, an Oklahoma Republican, famously lobbed a snowball
in the Senate as he denounced climate science. But these events don’t actually
disprove climate change.
While there have been some memorable storms in recent years,
winters are actually warming across the world. In the United States, average
temperatures in December, January and February have increased by about 2.5
degrees this century.
On the flip side, record cold days are becoming less common
than record warm days. In the United States, record highs now outnumber record
lows two-to-one. And ever-smaller areas of the country experience extremely
cold winter temperatures. (The same trends are happening globally.)
So what’s with the blizzards? Weather always varies, so it’s
no surprise that we still have severe winter storms even as average
temperatures rise. However, some studies suggest that climate change may be to
blame. One possibility is that rapid Arctic warming has affected atmospheric
circulation, including the fast-flowing, high-altitude air that usually swirls
over the North Pole (a.k.a. the Polar Vortex). Some studies suggest that these
changes are bringing more frigid temperatures to lower latitudes and causing weather
systems to stall, allowing storms to produce more snowfall. This may explain
what we’ve experienced in the U.S. over the past few decades, as well as a
wintertime cooling trend in Siberia, although exactly how the Arctic affects
global weather remains a topic of ongoing scientific debate.
Climate change may also explain the apparent paradox behind
some of the other places on Earth that haven’t warmed much. For instance, a
splotch of water in the North Atlantic has cooled in recent years, and
scientists say they suspect that may be because ocean circulation is slowing as
a result of freshwater streaming off a melting Greenland. If this circulation
grinds almost to a halt, as it’s done in the geologic past, it would alter
weather patterns around the world.
Not all cold weather stems from some counterintuitive
consequence of climate change. But it’s a good reminder that Earth’s climate
system is complex and chaotic, so the effects of human-caused changes will play
out differently in different places. That’s why “global warming” is a bit of an
oversimplification. Instead, some scientists have suggested that the phenomenon
of human-caused climate change would more aptly be called “global weirding.”
Wildfires and bad weather have always happened. How do we
know there’s a connection to climate change?
Extreme weather and natural disasters are part of life on
Earth — just ask the dinosaurs. But there is good evidence that climate change
has increased the frequency and severity of certain phenomena like heat waves,
droughts and floods. Recent research has also allowed scientists to identify
the influence of climate change on specific events.
Let’s start with heat waves. Studies show that stretches of
abnormally high temperatures now happen about five times more often than they
would without climate change, and they last longer, too. Climate models project
that, by the 2040s, heat waves will be about 12 times more frequent. And that’s
concerning since extreme heat often causes increased hospitalizations and
deaths, particularly among older people and those with underlying health
conditions. In the summer of 2003, for example, a heat wave caused an estimated
70,000 excess deaths across Europe. (Human-caused warming amplified the death
toll.)
Climate change has also exacerbated droughts, primarily by
increasing evaporation. Droughts occur naturally because of random climate
variability and factors like whether El Niño or La Niña conditions prevail in
the tropical Pacific. But some researchers have found evidence that greenhouse
warming has been affecting droughts since even before the Dust Bowl. And it
continues to do so today. According to one analysis, the drought that afflicted
the American Southwest from 2000 to 2018 was almost 50 percent more severe
because of climate change. It was the worst drought the region had experienced
in more than 1,000 years.
Rising temperatures have also increased the intensity of
heavy precipitation events and the flooding that often follows. For example,
studies have found that, because warmer air holds more moisture, Hurricane
Harvey, which struck Houston in 2017, dropped between 15 and 40 percent more
rainfall than it would have without climate change.
It’s still unclear whether climate change is changing the
overall frequency of hurricanes, but it is making them stronger. And warming
appears to favor certain kinds of weather patterns, like the “Midwest Water
Hose” events that caused devastating flooding across the Midwest in 2019.
It’s important to remember that in most natural disasters,
there are multiple factors at play. For instance, the 2019 Midwest floods
occurred after a recent cold snap had frozen the ground solid, preventing the
soil from absorbing rainwater and increasing runoff into the Missouri and
Mississippi Rivers. These waterways have also been reshaped by levees and other
forms of river engineering, some of which failed in the floods.
Wildfires are another phenomenon with multiple causes. In
many places, fire risk has increased because humans have aggressively fought
natural fires and prevented Indigenous peoples from carrying out traditional
burning practices. This has allowed fuel to accumulate that makes current fires
worse.
However, climate change still plays a major role by heating
and drying forests, turning them into tinderboxes. Studies show that warming is
the driving factor behind the recent increases in wildfires; one analysis found
that climate change is responsible for doubling the area burned across the
American West between 1984 and 2015. And researchers say that warming will only
make fires bigger and more dangerous in the future.
How bad are the effects of climate change going to be?
It depends on how aggressively we act to address climate
change. If we continue with business as usual, by the end of the century, it
will be too hot to go outside during heat waves in the Middle East and South
Asia. Droughts will grip Central America, the Mediterranean and southern
Africa. And many island nations and low-lying areas, from Texas to Bangladesh,
will be overtaken by rising seas. Conversely, climate change could bring
welcome warming and extended growing seasons to the upper Midwest, Canada, the
Nordic countries and Russia. Farther north, however, the loss of snow, ice and
permafrost will upend the traditions of Indigenous peoples and threaten
infrastructure.
It’s complicated, but the underlying message is simple:
unchecked climate change will likely exacerbate existing inequalities. At a
national level, poorer countries will be hit hardest, even though they have
historically emitted only a fraction of the greenhouse gases that cause
warming. That’s because many less developed countries tend to be in tropical
regions where additional warming will make the climate increasingly intolerable
for humans and crops. These nations also often have greater vulnerabilities,
like large coastal populations and people living in improvised housing that is
easily damaged in storms. And they have fewer resources to adapt, which will
require expensive measures like redesigning cities, engineering coastlines and
changing how people grow food.
Already, between 1961 and 2000, climate change appears to
have harmed the economies of the poorest countries while boosting the fortunes
of the wealthiest nations that have done the most to cause the problem, making
the global wealth gap 25 percent bigger than it would otherwise have been.
Similarly, the Global Climate Risk Index found that lower income countries —
like Myanmar, Haiti and Nepal — rank high on the list of nations most affected
by extreme weather between 1999 and 2018. Climate change has also contributed
to increased human migration, which is expected to increase significantly.
Even within wealthy countries, the poor and marginalized
will suffer the most. People with more resources have greater buffers, like
air-conditioners to keep their houses cool during dangerous heat waves, and the
means to pay the resulting energy bills. They also have an easier time
evacuating their homes before disasters, and recovering afterward. Lower income
people have fewer of these advantages, and they are also more likely to live in
hotter neighborhoods and work outdoors, where they face the brunt of climate
change.
These inequalities will play out on an individual,
community, and regional level. A 2017 analysis of the U.S. found that, under
business as usual, the poorest one-third of counties, which are concentrated in
the South, will experience damages totaling as much as 20 percent of gross
domestic product, while others, mostly in the northern part of the country,
will see modest economic gains. Solomon Hsiang, an economist at University of
California, Berkeley, and the lead author of the study, has said that climate
change “may result in the largest transfer of wealth from the poor to the rich
in the country’s history.”
Even the climate “winners” will not be immune from all
climate impacts, though. Desirable locations will face an influx of migrants.
And as the coronavirus pandemic has demonstrated, disasters in one place
quickly ripple across our globalized economy. For instance, scientists expect
climate change to increase the odds of multiple crop failures occurring at the
same time in different places, throwing the world into a food crisis.
On top of that, warmer weather is aiding the spread of
infectious diseases and the vectors that transmit them, like ticks and
mosquitoes. Research has also identified troubling correlations between rising
temperatures and increased interpersonal violence, and climate change is widely
recognized as a “threat multiplier” that increases the odds of larger conflicts
within and between countries. In other words, climate change will bring many
changes that no amount of money can stop. What could help is taking action to
limit warming.
What will it cost to do something about climate change,
versus doing nothing?
One of the most common arguments against taking aggressive
action to combat climate change is that doing so will kill jobs and cripple the
economy. But this implies that there’s an alternative in which we pay nothing
for climate change. And unfortunately, there isn’t. In reality, not tackling
climate change will cost a lot, and cause enormous human suffering and
ecological damage, while transitioning to a greener economy would benefit many
people and ecosystems around the world.
Let’s start with how much it will cost to address climate
change. To keep warming well below 2 degrees Celsius, the goal of the Paris
Climate Agreement, society will have to reach net zero greenhouse gas emissions
by the middle of this century. That will require significant investments in
things like renewable energy, electric cars and charging infrastructure, not to
mention efforts to adapt to hotter temperatures, rising sea-levels and other
unavoidable effects of current climate changes. And we’ll have to make changes
fast.
Estimates of the cost vary widely. One recent study found
that keeping warming to 2 degrees Celsius would require a total investment of between
$4 trillion and $60 trillion, with a median estimate of $16 trillion, while
keeping warming to 1.5 degrees Celsius could cost between $10 trillion and $100
trillion, with a median estimate of $30 trillion. (For reference, the entire
world economy was about $88 trillion in 2019.) Other studies have found that
reaching net zero will require annual investments ranging from less than 1.5
percent of global gross domestic product to as much as 4 percent. That’s a lot,
but within the range of historical energy investments in countries like the
U.S.
Now, let’s consider the costs of unchecked climate change,
which will fall hardest on the most vulnerable. These include damage to
property and infrastructure from sea-level rise and extreme weather, death and
sickness linked to natural disasters, pollution and infectious disease, reduced
agricultural yields and lost labor productivity because of rising temperatures,
decreased water availability and increased energy costs, and species extinction
and habitat destruction. Dr. Hsiang, the U.C. Berkeley economist, describes it
as “death by a thousand cuts.”
As a result, climate damages are hard to quantify. Moody’s
Analytics estimates that even 2 degrees Celsius of warming will cost the world
$69 trillion by 2100, and economists expect the toll to keep rising with the
temperature. In a recent survey, economists estimated the cost would equal 5
percent of global G.D.P. at 3 degrees Celsius of warming (our trajectory under
current policies) and 10 percent for 5 degrees Celsius. Other research
indicates that, if current warming trends continue, global G.D.P. per capita
will decrease between 7 percent and 23 percent by the end of the century — an
economic blow equivalent to multiple coronavirus pandemics every year. And some
fear these are vast underestimates.
Already, studies suggest that climate change has slashed
incomes in the poorest countries by as much as 30 percent and reduced global
agricultural productivity by 21 percent since 1961. Extreme weather events have
also racked up a large bill. In 2020, in the United States alone,
climate-related disasters like hurricanes, droughts, and wildfires caused
nearly $100 billion in damages to businesses, property and infrastructure,
compared to an average of $18 billion per year in the 1980s.
Given the steep price of inaction, many economists say that
addressing climate change is a better deal. It’s like that old saying: an ounce
of prevention is worth a pound of cure. In this case, limiting warming will
greatly reduce future damage and inequality caused by climate change. It will
also produce so-called co-benefits, like saving one million lives every year by
reducing air pollution, and millions more from eating healthier,
climate-friendly diets. Some studies even find that meeting the Paris Agreement
goals could create jobs and increase global G.D.P. And, of course, reining in
climate change will spare many species and ecosystems upon which humans depend
— and which many people believe to have their own innate value.
The challenge is that we need to reduce emissions now to
avoid damages later, which requires big investments over the next few decades.
And the longer we delay, the more we will pay to meet the Paris goals. One
recent analysis found that reaching net-zero by 2050 would cost the U.S. almost
twice as much if we waited until 2030 instead of acting now. But even if we
miss the Paris target, the economics still make a strong case for climate
action, because every additional degree of warming will cost us more — in dollars,
and in lives.
