Experts underestimate how fast Earth is warming, top climate scientist says in new study

A woman is silhouetted against the setting sun as triple-digit heat indexes continued in the Midwest Sunday, Aug. 20, 2023, in Kansas City, Mo.
A woman is silhouetted against the setting sun as triple-digit heat indexes continued in the Midwest Sunday, Aug. 20, 2023, in Kansas City, Mo.

Legendary climate scientist James Hansen, in a new study published Thursday, predicts that the Earth's temperature rise will accelerate in the upcoming decades and will reach 2 degrees Celsius above preindustrial temperatures by 2050. This is significantly more than the most common estimates from groups such as the Intergovernmental Panel on Climate Change, or IPCC, typically considered the planet's gold standard for climate forecasts.

According to Hansen's new study, the revised prediction is due to previous underestimations of the effects of greenhouse gases on the atmosphere, along with the effects of aerosols, which have acted to mask some of global warming.

Although the IPCC and other experts acknowledge the impact that aerosols have on the climate system – for example, NASA says that "if not for aerosol pollution, Earth would be even warmer than it already is" – Hansen and his co-authors say that that impact is "underestimated."

Specifically, Hansen told USA TODAY that the study's main point is that the Earth's climate is "more sensitive" to both greenhouse gases and air pollution than the IPCC realized.

Why does 2 degrees matter?

According to NASA, a "2-degree rise in global temperatures is considered a critical threshold above which dangerous and cascading effects of human-generated climate change will occur."

Hansen and his co-authors write in the paper that "impacts on people and nature will accelerate" as global warming increases toward the 2-degree threshold.

Beyond the temperature increase, the risks of weather and climate catastrophes also rise, as heat waves and death from extreme weather dramatically increase, according to an earlier United Nations scientific report.

In the American West, extreme fire weather will likely be more intense and last longer, NASA reports.

Exceptionally warm weather moved into the upper Midwest on Aug. 22 as a pedestrian walks at sunset in Oconomowoc, Wis. Climate scientist James Hansen  predicts that the Earth's temperature rise will accelerate in the upcoming decades.
Exceptionally warm weather moved into the upper Midwest on Aug. 22 as a pedestrian walks at sunset in Oconomowoc, Wis. Climate scientist James Hansen predicts that the Earth's temperature rise will accelerate in the upcoming decades.

Coastal cities threatened by sea level rise

NASA said that if warming reaches 2 degrees Celsius, more than 70% of Earth's coastlines will see sea level rise greater than 0.66 feet, "resulting in increased coastal flooding, beach erosion, salinization of water supplies and other impacts on humans and ecological systems."

We "must avoid 2 degrees global warming, which would otherwise result in the loss of our coastal cities near the end of this century," Hansen told USA TODAY.

Earth's climate 'more sensitive than usually assumed'

Using improved paleoclimate data, Hansen's new study finds that the Earth's climate "is more sensitive than usually assumed" to both carbon dioxide and aerosols.

The authors conclude that much of the expected greenhouse gas warming in the past century has been offset by the cooling effect of human-made aerosols – fine airborne particles found in air pollution. According to the study, aerosols have declined in amount since 2010 because of reduced air pollution in China and global restrictions on aerosol emissions from ships.

"This aerosol reduction is good for human health, as particulate air pollution kills several million people per year and adversely affects the health of many more people," Hansen said. "However, aerosol reduction is now beginning to unmask greenhouse gas warming that aerosol cooling hid."

The study authors term aerosol cooling a “Faustian bargain” because, as humanity eventually reduces air pollution, payment in the form of increased warming comes due.

What should we do?

The study recommends three actions humanity can undertake to avoid the 2-degree rise in global temperature:

(1) A global increasing price on greenhouse gas emissions accompanied by the development of abundant, affordable, dispatchable clean energy.

(2) East-West cooperation in a way that accommodates developing world needs.

(3) Conduct research and development for temporary actions to address Earth’s now enormous energy imbalance.

“We live on a planet with a climate characterized by delayed response, which is a recipe for intergenerational injustice,” Hansen concludes. “Young people need to understand this situation and the actions needed to assure a bright future for themselves and their children.”

The new study, "Global warming in the pipeline," appeared in the journal Oxford Open Climate Change, which is published by Oxford University Press.

This article originally appeared on USA TODAY: Global warming to accelerate faster than expected, James Hansen says