A Hotter Future Is Certain, Climate Panel Warns.
But How Hot Is Up to Us.
Some devastating impacts of global warming are now
unavoidable, a major new scientific report finds. But there is still a short
window to stop things from getting even worse.
The Dixie Fire, which destroyed one town and forced
thousands to flee their homes in Northern California, became the second largest
wildfire in state history on Sunday.
By Brad
Plumer and Henry Fountain
Aug. 9,
2021
Nations
have delayed curbing their fossil-fuel emissions for so long that they can no
longer stop global warming from intensifying over the next 30 years, though
there is still a short window to prevent the most harrowing future, a major new
United Nations scientific report has concluded.
Humans have
already heated the planet by roughly 1.1 degrees Celsius, or 2 degrees
Fahrenheit, since the 19th century, largely by burning coal, oil and gas for
energy. And the consequences can be felt across the globe: This summer alone,
blistering heat waves have killed hundreds of people in the United States and
Canada, floods have devastated Germany and China, and wildfires have raged out
of control in Siberia, Turkey and Greece.
But that’s
only the beginning, according to the report, issued on Monday by the
Intergovernmental Panel on Climate Change, a body of scientists convened by the
United Nations. Even if nations started sharply cutting emissions today, total
global warming is likely to rise around 1.5 degrees Celsius within the next two
decades, a hotter future that is now essentially locked in.
At 1.5
degrees of warming, scientists have found, the dangers grow considerably.
Nearly 1 billion people worldwide could swelter in more frequent
life-threatening heat waves. Hundreds of millions more would struggle for water
because of severe droughts. Some animal and plant species alive today will be
gone. Coral reefs, which sustain fisheries for large swaths of the globe, will
suffer more frequent mass die-offs.
“We can
expect a significant jump in extreme weather over the next 20 or 30 years,”
said Piers Forster, a climate scientist at the University of Leeds and one of
hundreds of international experts who helped write the report. “Things are
unfortunately likely to get worse than they are today.”
Not all is
lost, however, and humanity can still prevent the planet from getting even
hotter. Doing so would require a coordinated effort among countries to stop
adding carbon dioxide to the atmosphere by around 2050, which would entail a
rapid shift away from fossil fuels starting immediately, as well as potentially
removing vast amounts of carbon from the air. If that happened, global warming
would likely halt and level off at around 1.5 degrees Celsius, the report
concludes.
But if
nations fail in that effort, global average temperatures will keep rising —
potentially passing 2 degrees, 3 degrees or even 4 degrees Celsius, compared
with the preindustrial era. The report describes how every additional degree of
warming brings far greater perils, such as ever more vicious floods and heat
waves, worsening droughts and accelerating sea-level rise that could threaten
the existence of some island nations. The hotter the planet gets, the greater
the risks of crossing dangerous “tipping points,” like the irreversible
collapse of the immense ice sheets in Greenland and West Antarctica.
“There’s no
going back from some changes in the climate system,” said Ko Barrett, a
vice-chair of the panel and a senior adviser for climate at the National
Oceanic and Atmospheric Administration. But, she added, immediate and sustained
emissions cuts “could really make a difference in the climate future we have
ahead of us.”
The report,
approved by 195 governments and based on more than 14,000 studies, is the most
comprehensive summary to date of the physical science of climate change. It
will be a focal point when diplomats gather in November at a U.N. summit in
Glasgow to discuss how to step up their efforts to reduce emissions.
A growing
number of world leaders, including President Biden, have endorsed the goal of
limiting global warming to 1.5 degrees Celsius, though current policies in the
major polluting countries are still far off-track from achieving that target.
The 10 biggest emitters of greenhouse gases are China, the United States, the
European Union, India, Russia, Japan, Brazil, Indonesia, Iran and Canada.
The new
report leaves no doubt that humans are responsible for global warming,
concluding that essentially all of the rise in global average temperatures
since the 19th century has been driven by nations burning fossil fuels,
clearing forests and loading the atmosphere with greenhouse gases like carbon
dioxide and methane that trap heat.
The changes
in climate to date have little parallel in human history, the report said. The
last decade is quite likely the hottest the planet has been in 125,000 years.
The world’s glaciers are melting and receding at a rate “unprecedented in at
least the last 2,000 years.” Atmospheric levels of carbon dioxide have not been
this high in at least 2 million years.
Ocean
levels have risen 8 inches on average over the past century, and the rate of
increase has doubled since 2006. Heat waves have become significantly hotter since
1950 and last longer in much of the world. Wildfire weather has worsened across
large swaths of the globe. Bursts of extreme heat in the ocean — which can kill
fish, seabirds and coral reefs — have doubled in frequency since the 1980s.
In recent
years, scientists have also been able to draw clear links between global
warming and specific severe weather events. Many of the deadly new temperature
extremes the world has seen — like the record-shattering heat wave that
scorched the Pacific Northwest in June — “would have been extremely unlikely to
occur without human influence on the climate system,” the report says.
Greenhouse gas emissions are noticeably making some droughts, downpours and
floods worse.
Tropical
cyclones have likely become more intense over the past 40 years, the report
said, a shift that cannot be explained by natural variability alone.
And as
global temperatures keep rising, the report notes, so will the hazards.
Consider a dangerous heat wave that, in the past, would have occurred just once
in a given region every 50 years. Today, a similar heat wave can be expected
every 10 years, on average. At 1.5 degrees Celsius of global warming, those
heat waves will strike every 5 years and be significantly hotter. At 4 degrees
of warming, they will occur nearly annually.
Or take sea
level rise. At 1.5 degrees of warming, ocean levels are projected to rise
another 1 to 2 feet this century, regularly inundating many coastal cities with
floods that in the past would have occurred just once a century. But if
temperatures keep increasing, the report said, there is a risk that the vast
ice sheets in Antarctica and Greenland could destabilize in unpredictable ways,
potentially adding another three feet of sea-level rise this century in the
worst case.
Further
unpredictable changes may be in store. For example, a crucial ocean circulation
system in the Atlantic Ocean, which helps stabilize the climate in Europe, is
now starting to slow down. While the panel concluded with “medium confidence”
that the system was unlikely to collapse abruptly this century, it warned that
if the planet keeps heating up, the odds of such “low likelihood, high impact
outcomes” would rise.
“It’s not
like we can draw a sharp line where, if we stay at 1.5 degrees, we’re safe, and
at 2 degrees or 3 degrees it’s game over,” said Robert Kopp, a climate
scientist at Rutgers University who helped write the report. “But every extra
bit of warming increases the risks.”
Experts
have estimated that current policies being pursued by world governments will
put the world on track for roughly 3 degrees Celsius of warming by the end of
the century. That has ramped up pressure on countries to make more ambitious
pledges, beyond what they agreed to under an international climate agreement
struck in Paris in 2015.
If nations
follow through on more recent promises — like Mr. Biden’s April pledge to
eliminate America’s net carbon emissions by 2050 or China’s vow to become
carbon neutral by 2060 — then something closer to 2 degrees Celsius of warming
might be possible. Additional action, such as sharply reducing methane
emissions from agriculture and oil and gas drilling, could help limit warming
below that level.
“The report
leaves me with a deep sense of urgency,” said Jane Lubchenco, deputy director of
the White House Office of Science and Technology Policy. “Now is the critical
decade for keeping the 1.5 target within reach.”
While the
broad scientific understanding of climate change has not changed drastically in
recent years, scientists have made several key advances. Computer models have
become more powerful. And researchers have collected a wealth of new data,
deploying satellites and ocean buoys and gaining a clearer picture of the
Earth’s past climate by analyzing ice cores and peat bogs.
That has
allowed scientists to refine their projections and conclude with greater
precision that Earth is likely to warm between 2.5 degrees and 4 degrees
Celsius for every doubling of the amount of carbon dioxide in the atmosphere.
The new
report also explores in greater detail how global warming will affect specific
regions of the world. For example, while only one corner of South America to
date has had a detectable rise in droughts that can harm agriculture, such
damaging dry spells are expected to become much more common across the
continent if global average temperatures increase by 2 degrees Celsius.
The focus
on regional effects is one of the most important new aspects of this report,
said Valérie Masson-Delmotte, a climate scientist at University of Paris-Saclay
and a co-chair of the group that produced the report. “We show that climate
change is already acting in every region, in multiple ways,” she said.
Past
climate reports have focused mainly on large-scale global changes, which has
made it hard for countries and businesses to take specific steps to protect
people and property. To help with such planning, the panel on Monday released
an interactive atlas showing how different countries could be transformed as
global temperatures rise.
“It’s very
critical to provide society, decision makers and leaders with precise
information for every region,” Dr. Masson-Delmotte said.
The new
report is part of the sixth major assessment of climate science from the
Intergovernmental Panel on Climate Change, which was created in 1988. A second
report, set to be released in 2022, will detail how climate change might affect
aspects of human society, such as coastal cities, farms or health care systems.
A third report, also expected next year, will explore more fully strategies to
reduce greenhouse gas emissions and halt global warming.
Read more
about reports from the Intergovernmental Panel on Climate Change
Brad Plumer
is a climate reporter specializing in policy and technology efforts to cut
carbon dioxide emissions. At The Times, he has also covered international climate
talks and the changing energy landscape in the United States. @bradplumer
Henry
Fountain specializes in the science of climate change and its impacts. He has
been writing about science for The Times for more than 20 years and has
traveled to the Arctic and Antarctica. @henryfountain • Facebook
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