Hansen Vs. Mann — Is Global Warming Linear Or Exponential?

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James Hansen and Micheal Mann are giants in the climate science community. Hansen is the former NASA scientist who had the temerity to tell the Senate Energy Committee in 1988 that it was 99% certain the warming trend he and his fellow scientists had observed was not a natural variation but was caused by a buildup of carbon dioxide and other artificial gases in the atmosphere.

According to the New York Times, Hansen said in an interview after his testimony there was no ”magic number” that showed when the greenhouse effect was actually starting to cause changes in climate and weather, but added, ”It is time to stop waffling so much and say that the evidence is pretty strong that the greenhouse effect is here.”

Michael Mann is also a highly regarded climate scientist, and is the director of the Center for Science, Sustainability & the Media at the University of Pennsylvania. Mann has contributed to the scientific understanding of historic climate change based on the temperature record of the past thousand years. He and his colleagues introduced the now famous “hockey stick” graph that showed a steep rise in average global temperatures beginning with the advent of the Industrial Revolution.

James Hansen & Climate Forcings

Credit: Oxford University Press

In research published on November 2, 2023 in the journal Oxford Open Climate Change, James Hansen and his colleagues present the argument that the models and predictions offered by the International Panel on Climate Change are too conservative. In fact, Hansen’s group says their research shows that there are factors already embedded in the Earth’s atmospheric and aquatic environments which will lead to significant increases in average global temperatures in the near future — larger increases than IPCC forecasts.

The study is long and extremely detailed. It examines the average temperature of the Earth over the past 66 million years, including a time when carbon dioxide levels were half what they are today and the Earth was on its way to becoming a frozen ball of ice. It identifies how natural perturbations like oscillations in the Earth’s orbit and sunspot activity affect the Earth’s climate.

The upshot of all this is that despite all those natural influences, the amount of what scientists call “forcings” attributable to human activities will lead to average global temperatures rising far higher and sooner than IPCC protections suggest. Below is the summary.

“Climate change is characterized by delayed response and amplifying feedbacks. Delayed response makes human-made climate forcing a threat to today’s public and future generations because of the practical difficulty of reversing the forcing once consequences become apparent. Feedbacks determine climate sensitivity to any applied forcing. We find that Earth’s climate is very sensitive — more sensitive than the best estimate of the Intergovernmental Panel on Climate Change — which implies that there is a great amount of climate change ‘in the pipeline.’ Extraordinary actions are needed to reduce the net human-made climate forcing, as is required to reduce global warming and avoid highly undesirable consequences for humanity and nature.”

We Are Damn Fools! — James Hansen

“We would be damned fools and bad scientists if we didn’t expect an acceleration of global warming,” Hansen told The Guardian. “We are beginning to suffer the effect of our Faustian bargain. That is why the rate of global warming is accelerating.”

Hansen noted there is an imbalance between the energy coming in from the sun versus the energy going outward from the Earth has “notably increased.” In fact, it has almost doubled over the past decade. That increase could result in a disastrous amount of sea level rise for the world’s coastal cities.

The new research, comprising peer reviewed work of Hansen and more than a dozen other scientists, argues that this imbalance, the Earth’s greater climate sensitivity, and a reduction in pollution from shipping — which has cut the amount of airborne sulfur particles that reflect incoming sunlight — are causing an escalation in global heating.

“We are in the early phase of a climate emergency,” Hansen and his colleagues write. “Such acceleration is dangerous in a climate system that is already far out of equilibrium. Reversing the trend is essential — we must cool the planet — for the sake of preserving shorelines and saving the world’s coastal cities.”

Is Geo-Engineering The Answer?

To deal with this crisis, Hansen and his colleagues advocate for a global carbon tax as well as spraying sulfur dioxide into the upper atmosphere in order to deflect heat away from the planet to artificially lower the world’s temperature, a process known as geoengineering.

That idea has been widely criticized by other members of the scientific community, who point out that the process will be very expensive — on the order of tens of trillions of dollars. In addition, there could be unknown and unknowable negative effects when and if the program is terminated. Nevertheless, Hansen and a small group of  climate scientists warn the world is running out of time and options to avoid catastrophic temperature growth.

Then there are the geopolitical implications. What if China decides the best way to preserve its climate is to cast a sulfur dioxide shadow over North America? If history is any guide, if an idea can be weaponized, humans will find a way to do so. But the real danger is that the Earth’s environment is so complex, involving trillions of interactions, from solar flares to a butterfly fluttering its wings high in the Andes, that no one can comprehend them all. Adding yet another variable could lead to unpredictable results, some of which could be quite destructive.

Hansen said that while cutting emissions should be the highest priority, “thanks to the slowness in developing adequate carbon-free energies and failure to put a price on carbon emissions, it is now unlikely that we can get there — a bright future for young people — from here without temporary help from solar radiation management.”

Our Shrinking Carbon Budget

Another report this week found that the carbon budget to limit the world to 1.5C of heating is now nearly exhausted due to the continued burning of fossil fuels and deforestation. It says the Earth’s environment can only absorb another six years of emissions from burning fossil fuels before a tipping point is reached that could send global temperatures soaring. And yet, the United States is gloating about being the largest exporter of liquified natural gas  in the world and planning to build six more LNG terminals in the Gulf of Mexico.

Professor Joeri Rogelj of Imperial College London is one the authors of the study. He told The Guardian, “The budget is so small, and the urgency of meaningful action for limiting warming is so high, [that] the message from [the carbon budget] is dire. Having a 50% or higher likelihood that we limit warming to 1.5C is out of the window, irrespective of how much political action and policy action there is.” He said it was “remarkable” how much risk humanity appeared willing to take with global heating.

Dr. Chris Smith of the International Institute for Applied Systems Analysis in Austria, who was also part of the study, said “Governments can control the emissions but, at the moment, they have not done so. This is why we have an ever-shrinking carbon budget. We are not saying we only have six years to solve climate change – absolutely not. If we are able to limit warming to 1.6C or 1.7C, that’s a lot better than 2C. We still need to fight for every 10th of a degree.”

Is Global Warming Accelerating?

But while scientists are clear about this being part of an upward trend of global heating, there is as yet no agreement that this trend is accelerating. Michael Mann said that Hansen and his co-authors are “very much out of the mainstream” in identifying an acceleration in surface heating that has “continued at a remarkably constant rate for the past few decades.” He added that cuts to shipping emissions have only a tiny effect on climate systems and that calls for solar geoengineering are misguided and a “very slippery slope.”

Bärbel Hönisch, a paleoclimatologist at Columbia University, said she had “some reservations” about the certainties expressed in Hansen’s research about the state of the Earth’s climate millions of years ago, which helps predict the consequences of warming today. “I would be a little more reserved but they may well be correct. It’s a nicely written paper. It raises a lot of questions that will trigger a lot of research that will bring our understanding forward.”

Some other researchers are less skeptical of Hansen’s dire warning of supercharged global heating, highlighting his previous prescient warnings about the climate crisis that have largely played out due to decades of inaction to stem the use of fossil fuels.

“I think Hansen’s contention that the IPCC has underestimated climate sensitivity somewhat will prove to be correct,” said Rob Jackson, a Stanford University scientist and chair of the Global Carbon Project. “It’s hard to know what’s unlikely any more in terms of warming. No fossil fuel has declined in use yet globally, not even coal. I think Hansen’s pessimism is warranted. He stood up 35 years ago and sounded the alarm — and the world mostly ignored him, and all of us.”

The Takeaway

There seems to be little hope these latest reports will have any more impact than those previous studies did. The world is in thrall to fossil fuel companies and no amount of information about how their activities are risking a climate catastrophe seems about to alter the course of history.

The upcoming COP 28 summit in Dubai may be the world’s last chance to respond appropriately to the looming climate crisis. But being set in a petro-state and chaired by an oil executive gives little hope for much more than pious pronouncements and impassioned oratory.

We are like heroin addicts — unable to curb our desires. This is not likely to end well for any of us, not even the ultra wealthy cosseted in their underground lairs in New Zealand, sending endless texts and tweets when there is no one left to answer them. How sad we must look to anyone watching from beyond the Earth. Perhaps Humanity is little more than a cosmic joke.

Yip Harburg, the lyricist who wrote the words to “Over The Rainbow,” was also a satirist with a keen wit. He penned a little ditty once that went like this:

God made the world in six days flat.

On the seventh he said, “I’ll rest.”

So he let the thing into orbit swing

To give it a dry run test.

A billion years went by,

Then he took a look at the whirling blob.

His spirits fell as He said,

“Oh well. It was only a six day job.”


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