CLIMATE CRISIS May Be Worse Than You Think, Says James Hansen, Part 2

Are Aerosols Driving The Current Surge of Global Warming?

From an Article by Bob Berwyn, Inside Climate News, 11/2/23

For several years, James Hansen and Leon Simons have proposed that the recent and ongoing surge in a wide range of global climate indicators — not just average global temperatures — may be driven in large part by a sharp reduction in tiny sulfuric particles produced by burning shipping fuels and other fossil fuels, and by other industrial processes.

Those aerosol particles, spewed into the atmosphere in massive quantities since the start of the industrial revolution, often make clouds brighter and more persistent, so they reflect more of the sun’s incoming heat energy back to space. While carbon dioxide and other greenhouse gases have been warming the planet since at least 1850, other byproducts of burning fossil fuels were cooling the planet at the same time, although the effects of aerosols only last for a fraction of the time that the heat-trapping gases persist in the atmosphere.

That basic idea is not controversial, but Hansen’s new research about the relative strengths of those competing effects diverges from many other studies by suggesting the cooling effect has been underestimated so that as sulfur aerosols and their effects on clouds are reduced, temperature will increase more than expected.

How clouds will change in the decades ahead, and their interaction with aerosols, remains the single greatest uncertainty in making accurate projections for future temperature increases, according to most climate scientists. Several key satellite instruments that could have helped answer that question never made it into orbit in the 1980s and 1990s, despite repeated requests, Hansen said.

In 2009 James Hansen published Storms of My Grandchildren as a climate prophecy about what kind of world is still possible for children born in the 21st century, and is currently finishing a book called Sophie’s Planet, written as a series of letters to his granddaughter with a similar theme—how the choices we make right now will affect future generations.

Hansen retired from NASA and now heads the Climate Science, Awareness and Solutions think tank at Columbia University’s Earth Institute. He remains active in public policy advocacy and has also lent his climate science expertise in several legal cases due to his belief—shared by Abramoff, Kalmus and thousands of other scientists—that knowledge confers a moral imperative to act.

Gavin Schmidt, who replaced Hansen as head of NASA’s global Institute for Space Studies, said those missions to study aerosol composition and change should have been higher priorities.

“Jim and others did have to fight hard to get an aerosol polarimeter on the GLORY mission, which would have gone a long way to helping,” Schmidt said. “Unfortunately that did not reach orbit due to a faulty faring on the rocket, which turned out to be due to fraud in the supply chain.”

Gavin Schmidt said a new mission called PACE (short for Plankton, Aerosol, Cloud, ocean Ecosystem) could quickly reduce the uncertainties surrounding the effects of aerosols on the climate. That satellite should be in orbit within the coming year. Copernicus, the European Union climate change service, is also launching a new satellite, EarthCARE, also with the goal of measuring the relationship of aerosols, clouds and precipitation to how much of the sun’s radiation reaches Earth to drive global heating.

Absent those data, the new study used a process of elimination to again show reductions in sulfur aerosols were triggering accelerated warming. Comparisons with past climate periods hold some of the clues, showing, for example, that reefs along the Yucatán Peninsula grew upward and shoreward in giant spurts over the course of just a few decades, about 100,000 years ago during the late Eemian geological era. That, Hansen said, is another warning sign that parts of Earth’s climate system, and particularly ice sheets and ice shelves, are more sensitive to warming than we think.

“The IPCC system doesn’t acknowledge the degree to which the aerosol forcing will affect the climate in the next few decades, probably more than anything else,” Simons said. “We hope we’re wrong.”

Deep Divides Over Climate Communication

The paper drew criticism when it was made public as a draft, shining a light on a long-running rift in the climate science community about how to communicate relative levels of certainty about global warming and its impacts.

The sharp backlash to the final version published today, as well as Hansen’s direct critique of the IPCC, suggest that the divide is only growing deeper. In a commentary Hansen published describing the new paper, he wrote that reviewers of some of his previous papers have been reticent to endorse full-throated warnings about global warming by choosing, for example, to eliminate words like “dangerous” in a description of the documented climate impacts of 2 degrees Celsius of warming.

But several well-known climate scientists said Hansen is confusing reticence with insistence on accuracy and robustness. “His commentary is terrible,” said Piers Forster, director of the Priestley Centre for Climate Futures at the University of Leeds, and lead author of the section of the most recent IPCC report that covered climate feedbacks and climate sensitivity. “This is simply a very bad hotchpotch of a paper made out to be a new assessment of climate sensitivity and critique of IPCC,” Forster said. “It is nothing of the sort.” Instead, Forster said the paper is a combination of historical perspectives, geographic modeling and Hansen’s opinions.

The high climate sensitivity estimates cited in Hansen’s paper “all seem quite subjective and not justified by observations, model studies or literature,” he said. “They portray their paper as an alternative but it doesn’t have rigor, systematic analysis or comprehensive literature review. It also does a great disservice to the hundreds of scientists from around the world that give many years of their lives to the IPCC process.”

Kevin Trenberth, a distinguished professor emeritus with the National Center for Atmospheric Research, said he was surprised the new paper was published, noting that the journal is relatively obscure. “I think it is likely wrong,” Trenberth said. “Hansen has never been involved in the IPCC in any capacity, even as a reviewer. He is not at all collegial and he tends to ignore legitimate criticism. He moves papers around until they get published. He stuffs papers full of extraneous stuff that would not be publishable by itself.”

Trenberth said the new paper relies on an estimate of paleoclimate sensitivity that was proven wrong by a 2021 study that modeled ancient warm and cold periods, providing a way to accurately assess the climate impact of industrial age greenhouse gas emissions. He said Hansen’s team also seems to have ignored increasing water vapor caused by global warming as a factor in the recent warming surge.

“Water vapor is a major feedback,” he said. “As temperatures go up so does the water-holding capacity of the atmosphere,” which amplifies global warming.

Hansen and Simons are undeterred by the controversy swirling around their research and remain convinced they have a duty to warn and to make policy recommendations, some of which are controversial. Hansen advocates for speeding up decarbonization by instituting a global price on carbon, using more nuclear energy and accelerating the deployment of renewable energy. And he said scientists need to study various forms of geoengineering, including the deliberate dispersal of chemicals in the atmosphere to reflect a small percentage of incoming solar energy, or the brightening of large areas of ocean clouds by spraying salt mists into the sky with a fleet of robot boats.

Those ideas are still highly controversial in the science community, but Hansen said that, because the current generation has painted itself into a tight climate corner, we owe it to future generations to give them as many informed choices as possible, and studying geoengineering is part of that.

“We have to recognize we’re geoengineering the planet right now,” Hansen said. “This is what we’re doing by putting these huge amounts of greenhouse gas into the atmosphere,” which is warming the planet “at a greater rate than has ever occurred in the Earth’s history, as far as we know.” That warming has to be slowed, and that will probably require reflecting sunlight because of how hard it is to remove greenhouse gases from the atmosphere once they are there, he added.

Simons said there is a need for specialized science teams to determine if rapid sulfur aerosol reductions are indeed causing the current global temperature spike and how the sudden drop of pollution and the temperature increase interact to affect monsoon rainfall, as well as ocean currents and large-scale atmospheric patterns.“There are no easy choices in this,” Simons recently posted on the social media site X, formerly known as Twitter. “How much warming will the world accept? And how fast can the rate of warming be until we are unable to adapt? And will we have the stability of global governance to face these accumulating challenges?”