In the run-up to Donald Trump’s inauguration, many climate experts are expressing concern that his views and those of his senior appointees are at odds with mainstream climate science. They’re grimly preparing to re-enter the fray of last-decade’s “climate wars”, which saw scientific knowledge about global warming come under intense and sustained attack.
I am as concerned as anyone by politicians’ newfound aversion to evidence – pioneered, embarrassingly, by populists in the UK. Obviously, if politicians say things that are simply false, it is our duty as scientists to point that out.
But we should also point out what they are not saying, which suggests that Trump and his appointees accept much more of the scientific evidence for human-induced climate change than they are prepared to let on – and, crucially, much more than most of their supporters probably think they do: a case of the footsoldiers not realising that their generals have abandoned them. And what those generals accept is already more than enough to justify continuing the relatively modest climate goals of the Obama administration.
I appreciate this line is asking a lot of Trump’s opponents: to characterise the president-elect and his appointees as straightforwardly anti-science seems like a political open goal. The problem is, it may also be an own goal.
Trump’s nominee for secretary of state, former ExxonMobil boss Rex Tillerson, claims “our ability to predict that effect [of greenhouse gas emissions] is very limited”. But he carefully avoids saying whether he means effect on the global energy budget (which is nailed down to within 10% or so), effect on global temperatures (which is predictable, and predicted, within a factor of two), or effect on the weather in Washington DC. So when a helpful journalist adds that 97% of climate scientists disagree with him, all that members of the public hear is that 97% of climate scientists are idiots: of course climate prediction is uncertain.
So, what are these facts on which Trump and colleagues are so carefully silent? First, the idea that there is no connection between humanity’s greenhouse gas emissions and rising temperatures seems to have been quietly abandoned. Trump himself acknowledges “some connectivity”. Tillerson has conceded “an effect”, while Scott Pruitt, who Trump is proposing to lead the Environment Protection Agency, has called for a debate about the “degree and extent” of human-induced climate change, not whether it exists at all. This is a long way from Senator James Inhofe and his snowball.
Second, no one outside the wilder fringes of the internet is publicly arguing that 3-4℃ of human-induced global warming (far beyond the range of climate fluctuations since the last ice age) is “acceptable”. Perhaps some individuals believe it in private, but Tillerson has certainly been advised not to express this view in public lest Exxon gets landed with the bill for relocating the population of Bangladesh. So there may be more consensus than meets the eye on what constitutes “dangerous interference” in the climate system.
Third, everyone also agrees that how the climate responds to global emissions is uncertain, and how policies affect emissions is even more so. So as far as today’s policies are concerned, whether we are aiming to stabilise temperatures at 2.5℃ above pre-industrial levels, or the 2015 Paris Agreement goal of “well below 2℃”, is largely moot: what matters is that we are aiming to stabilise temperatures at some point this century, rather than settling for indefinite warming.
And finally, no-one is contesting the other key conclusion of Paris, that stabilising the climate requires net global carbon dioxide emissions to be reduced to zero. This is significant precisely because there are other ways of stabilising global temperatures, such as “solar radiation management” where reflective particles are inserted into the upper atmosphere. I am not aware of anyone in the incoming administration advocating such geo-engineering – unsurprisingly, since to do so would acknowledge that climate change is a present danger requiring a globally coordinated response.
Put together, these facts logically imply that net global greenhouse gas emissions need to be reduced to zero sometime this century – which is not that far from the UNFCCC position. Temperatures have already risen by about 1℃ since the mid-19th century (and, again, no one seems to be disputing this any more). If we are to stabilise warming below 2℃, every 0.1℃ of additional warming from now on must be matched by emission reductions equal to, on average, 10% of today’s emission rate. At the rate the Earth has been warming since the 1970s, 0.1℃ takes less than a decade, so 10% per 0.1℃ means emission reductions of 1-2% per year: and the longer we put them off, the steeper the required cuts become.
Perhaps Pruitt and Tillerson really believe that reductions at the modest end of this uncertainty range are all that’s required. We should all hope they are right (although it would be nice to see the evidence), because that would mean current plans might be just enough to meet the long-term temperature goals agreed in Paris, , rather than woefully inadequate. But it hardly makes a strong case for investing in new coal-fired power plants.
The Paris Agreement and the Obama government’s Clean Power Plan were hard-won successes. But, though it may seem disloyal to point this out, both actually had relatively modest goals that are more than justified even by the new administration’s more sanguine attitude to the climate problem.
Both scientists and liberal journalists may be reluctant to give the incoming administration credit for being right about anything. Much of what they are saying is indeed demonstrably at odds with scientific evidence. When Tillerson suggested that scientists were equally split on whether it was possible to trace a link between greenhouse gas emissions and some classes of extreme weather event, he was simply out of date.
But what they are not prepared to say tells a different story – one that shows how far the debate has moved on even among the most ardent disbelievers. Sometimes, as Sherlock Holmes would say, the most important clue is the dog that doesn’t bark.