However, there is now some emerging evidence via an analysis of palo-climatology data that this may be way too optimistic and that the actual range could potentially be in the range of 4.78C to 7.36C by 2100. That is rather disturbing because such a rapid shift within that range is not only unprecedented over the past 1 million years. We are no longer looking at a challenging future, but instead a possible apocalyptic one.
If this is really what we face, then a book that perhaps lays out where such a temperature increase would take us is “Six Degrees: Our Future on a Hotter Planet.” by Mark Lynas. There he lays it all out …
The book explains how the release of methane hydrate and the release of methane from melting permafrost could unleash a major extinction event. Carbon cycle feedbacks, the demise of coral, the destruction of the Amazon rainforest, and extreme desertification are also described, with five or six degrees of warming potentially leading to the complete uninhabitability of the tropics and subtropics, as well as extreme water and food shortages, possibly leading to mass migration of billions of people.
Let’s pause, step back and take a look at the paper itself that lays out this possibility.
Nonlinear climate sensitivity and its implications for future greenhouse warming
The paper, published a few days ago in AAAS has an abstract that explain it as follows …
Global mean surface temperatures are rising in response to anthropogenic greenhouse gas emissions. The magnitude of this warming at equilibrium for a given radiative forcing—referred to as specific equilibrium climate sensitivity (S)—is still subject to uncertainties. We estimate global mean temperature variations and S using a 784,000-year-long field reconstruction of sea surface temperatures and a transient paleoclimate model simulation. Our results reveal that S is strongly dependent on the climate background state, with significantly larger values attained during warm phases. Using the Representative Concentration Pathway 8.5 for future greenhouse radiative forcing, we find that the range of paleo-based estimates of Earth’s future warming by 2100 CE overlaps with the upper range of climate simulations conducted as part of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Furthermore, we find that within the 21st century, global mean temperatures will very likely exceed maximum levels reconstructed for the last 784,000 years. On the basis of temperature data from eight glacial cycles, our results provide an independent validation of the magnitude of current CMIP5 warming projections.
There is no paywall, and so you can read the full paper yourself.
Basically, the paper uses paleo-climate data to point out that when the planet became warmer it also became more sensitive to greenhouse gas emissions. That sensitivity needs to be considered when projecting the future in the climate models. They use standard RCP 8.5 for that, and that yields the higher projections.
Dr Tobias Friedrich, one of the paper’s authors is quoted as explaining …
Our results imply that the Earth’s sensitivity to variations in atmospheric carbon dioxide increases as the climate warms.
Currently, our planet is in a warm phase – an interglacial period – and the associated increased climate sensitivity needs to be taken into account for future projections of warming induced by human activities.
The only way out is to reduce greenhouse gas emissions as soon as possible.
What do the Subject Matter Experts think of this paper?
The publication of such papers is about having a conversation with the community and so it should come as no surprise to observe that this is controversial – some agree and so do not.
An article on this within the UK’s Independent has a few interesting quotes …
Professor Michael Mann, of Penn State University in the US, who led research that produced the famous “hockey stick” graph showing how humans were dramatically increasing the Earth’s temperature, told The Independent the new paper appeared “sound and the conclusions quite defensible”.
“And it does indeed provide support for the notion that a Donald Trump presidency could be game over for the climate,” he wrote in an email.
…Dr Ganopolski, of the Potsdam Institute for Climate Impact Research in Germany, suggested their findings meant it would be harder to prevent the world entering dangerous global warming of 2C or above.
“Our results mean it is not impossible to stay within 2C but it probably – if we are right and climate sensitivity is higher than this – would require even strong cuts in carbon emissions,” he said.
“Whether it’s feasible politically … I believe it is feasible technically.
“It would be really good to stay below 1.5C or close to that, whether it’s feasible I’m probably a bit sceptical about that.”
Commenting on the paper, Professor Eric Wolff, of Cambridge University, said using data from the past was a “powerful way of understanding the climate”.
But he noted the authors had used different ways of estimating average global temperature, some of which had produced “a lower range of values”.
“The estimates of temperature in this paper are subject to large uncertainties, and therefore the range of estimates for 2100 is also very wide,” Professor Wolff said.
“Still, it’s encouraging that it overlaps with model estimates and confirms that the emission reductions promised in Paris are essential to avoid unacceptable climate changes.”
Trump
With his declared intent to walk down the “do nothing” path, we now face a Trump presidency that is an existential threat. He is old enough to not have to face the consequences, but in the not too distant future, our children will.
One of the biggest ever environmental campaigns has been launched by a group of the world’s most eminent scientists and environmentalists in an ’emergency’ effort to convince the President-elect, Donald Trump, that global warming is real before he becomes US President in January.
Mr Trump, who described climate science as a “hoax” perpetrated by China, has already appointed a prominent climate change denier, Myron Ebell, to a key environmental post and promised that he will rip up the landmark Paris Agreement climate deal when he enters the White House.
… Among those now preparing for arguably the most important campaign ever designed to change the mind of a single individual in modern history is the Sierra Club
… the American Association for the Advancement of Science (AAAS) is bringing together leading scientists from across the US to urge Mr Trump to listen to the evidence, rather than accept the testimonies of conspiracy theorists and fossil fuel lobbyists.
There is hope.
It is distinctly possible that the argument that might persuade him is a financial one and not a evidence-based one. What is also clear is that he did indeed play switch and bait with the voters. He wanted the status and so would tell them what they wanted to hear in order to manipulate, it is who he is.
I’m not making this up, because clearly much of what he said is being rowed rapidly back. We learned via his interview in the Washington Post and in a 60 Minutes and other places that Obamacare stays, he will instead improve it. Also, “drain the swamp!” is now revealed to be political theatre as he pulls in longtime corporate lobbyists. Apparently he will even be calling on both Obama and Bill Clinton for advice and guidance.
So in a climate change context there is some hope, but the risks are still huge.
Bottom Line: Doing nothing is not an option, but is also not yet inevitable.