James Hansen, et al: "A Miracle Will Occur" Is Not Sensible Climate Policy

[OKIsItJustMe]

“A Miracle Will Occur” Is Not Sensible Climate Policy

07 December 2023

James Hansen, Pushker Kharecha, Makiko Sato

The COP28 Chairman and the United Nations Secretary General say that the goal to keep global warming below 1.5°C is alive, albeit barely, implying that the looser goal of the 2015 Paris Agreement (to keep warming well below 2°C) is still viable. We find that even the 2°C goal is dead if policy is limited to emission reductions and plausible CO₂ removal. IPCC (the Intergovernmental Panel on Climate Change, which advises the UN) has understated global warming in the pipeline and understated fossil fuel emissions in the pipeline via lack of realism in the Integrated Assessment Models that IPCC uses for climate projections. Wishful thinking as a policy approach must be replaced by transparent climate analysis, knowledge of the forcings that drive climate change, and realistic assessment of policy options. The next several years provide a narrow window of time to define actions that could still achieve a bright future for today’s young people. We owe young people the knowledge and the tools to continually assess the situation and devise and adjust the course of action.

Our approach to analysis of global climate change, as described in Global Warming in the Pipeline,¹ puts comparable emphasis on (1) Earth’s paleoclimate history, (2) global climate models (GCMs), (3) modern observations of climate processes and climate change. One purpose of the Pipeline paper was to distinguish between this approach and that of IPCC, which puts principal emphasis on GCMs. GCMs are an essential tool, but the models must be consistent with Earth’s history and the projections of future climate must employ plausible scenarios for energy use and for the climate forcings that drive climate change.

Policy implications of climate science can be grasped from a basic understanding of the human-made forcings that are driving Earth’s climate away from the relatively stable climate of the Holocene (approximately the past 10,000 years). Our task is to provide understandable quantification of climate forcings and changes that will be needed to maintain a hospitable climate. Concerned public, including policymakers, must learn to appreciate basic graphs that summarize real-world data, because these must provide the basis for policy discussion.

1. CLIMATE SCIENCE

There are two major climate forcings: human-made greenhouse gases (GHGs) and aerosols (fine airborne particles). GHGs reduce Earth’s thermal (heat) radiation to space and are the main cause of global warming. Aerosols reflect sunlight to space, mainly via their effect as condensation nuclei for clouds; more nuclei lead to smaller cloud drops and brighter, longerlived, clouds. Aerosols thus cause a global cooling that partially offsets GHG warming.

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[OKIsItJustMe]

1. Response to Michael Mann's Criticism of "Global Warming in the Pipeline"

Michael Mann says that he doesn’t see any acceleration of global warming. Some people would say that the acceleration is already apparent, but the level to which global temperature rises by next May and then falls in the next La Nina, will firmly settle that matter.

Mike also says that he doesn’t see an increase in the rate of heat uptake by the ocean. Fig. 4 (by Li et al.) in our prior communication²¹ shows that there is evidence of increased heat uptake even in the long-term in situ ocean data, which have large error bars because of the difficulty in obtaining adequate coverage of the global ocean with consistent instrument calibrations. However, our analysis refers to the changes underway in the 21st century, when we have much more precise data on Earth’s energy imbalance from the combination of in situ Argo ocean data and satellite CERES data (Fig. 7 above). The increase of absorption of solar radiation by Earth and the increase of Earth’s energy imbalance are much larger than the measurement uncertainty. The measurements need to be continued!⁵³

Mike also says that our paper is “wrong” because nations and industries and businesses are promising to go to zero emissions or net zero emissions in the future (sometimes in the far future, when the promiser will be dead or at least out of office). Leaving aside whether the promisers can all be trusted to deliver and whether their concept of “net zero” is really zero (very big assumptions!), the present global warming and planetary energy imbalance assure that we will hit 2°C global warming. Present knowledge of the consequences of ZEC (Zero Emissions Commitment, the change in global mean temperature expected to occur following cessation of net CO2 emissions), MacDougall et al.,⁵⁴ indicates an approximate stabilization of global temperature from the time at which ZEC is achieved. As for the realism of the assumptions of near-term achievement of ZEC, one would be wise to read the opinions of Dyke, Watson and Knorr,⁵⁵ who have had the real-world experiences needed to grasp the nature of the present situation.

[orthoclad]

2. That "miracle" model

fits a lot of people's expectations.
It used to be that "the scientists will save us", but now that factual stuff is out of fashion, some god will step in. Either by saving us, or by causing the Rapture where a few thousand chosen will be lifted to heaven, and to hell with the rest of us.

[OKIsItJustMe]

4. There is another source of the "miracle;" AI

Naturally, we don’t know exactly how AI will solve the problem of climate change, that’s why we need AI to solve it, because it’s beyond our comprehension. OK, so, it’s not really beyond our comprehension, we just don’t like the obvious answer — haven’t liked it for 50-odd years.

[NickB79]

3. It's the South Park underpants gnome model

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