Recent White House initiatives suggest that addressing climate change has risen to the policy forefront of government at the presidential level for the first time in US history. Last week President Biden convened an online international meeting of heads of state on the issue and committed the US to a dramatic effort to reduce greenhouse gas emissions to a level of 50 percent of emissions in 2005 by the year 2030, which will require unprecedented action and cooperation between government and major industries.

By and large, the public’s mood has shifted from one of skepticism to support, but because the issue is so deeply embedded in scientific predictions whose details are often absent in popular discussions, statements from prominent scientists have great potential to influence the debate.

As a theoretical physicist whose primary research has been in what is often called “fundamental physics” I am acutely aware that my colleagues can project an air of superiority in being dismissive of other disciplines and the scientists who labor in them. My late friend and colleague Freeman Dyson was an example. Freeman was one of the smartest physicists I have known, and we spoke at length on a few occasions about climate change. His views, while creative and novel, like almost all of his ideas, were nevertheless woefully uninformed. I suspect he felt that because he was smarter than climate scientists, he distrusted their work. One of his heroes, and one of my heroes, Richard Feynman often had a similar attitude, and insisted in reinventing the wheel on numerous occasions rather than rely on the results of others. Another brilliant colleague, the late Harvard Prof. Sidney Coleman, once gave Feynman useful advice, which he ignored at cost to his own work at times: “Not everyone else is a bozo!”

That brings me to another colleague, Steve Koonin, a distinguished nuclear theorist from Caltech who, since 2014, when he published his first editorial on the subject in the Wall Street Journal, has continued to argue along the lines of his column’s title, “Climate Science is not Settled.” Most recently he has written a new book, Unsettled, which has already generated a buzz due in part to a long Wall Street Journal column about his views, and last week reached #3 on Amazon in advance of publication.

Koonin’s voice carries significant clout. He was undersecretary of Energy in the Obama Administration, provost at Caltech, and also chief scientist at BP. He accepts the reality that human induced global warming is a reality and that the Earth has indeed warmed by 1.4⁰C since 1900. His arguments appear to represent a measured voice of reason, warning against over-stepping the bounds of “settled” science when developing public policy, which he argues is what is happening with climate change policies.

Here, however, he is doing a disservice to both climate science and the public.

In the first place, no science is ever completely settled. That is the beauty of science. Newton’s classical law of gravity, which does a beautiful job of describing most phenomena on human scales, was supplanted by General Relativity. General Relativity in turn is likely to be supplanted by a new quantum theory, perhaps based on string theory.

But scientific revolutions don’t do away with well-established science that has already survived the test of experiment. They add to it. And while there is much about the Earth and the Universe we do not understand, that does not mean we understand nothing.

The basic physics underlying global climate change is clear and has been clear for over 100 years, beginning with Joseph Fourier in 1824, and following on to John Tyndall in the 1850s, followed by Svante Arrhenius, the Nobel prizewinning Swedish chemist in 1896. The details, including radiative transfer through the atmosphere, required modern methods, but have confirmed the fundamental science.

Theoretical predications have been confirmed by observations. The measured global temperature increase of 1.4⁰C since 1900 is consistent with the additional heat input of between 1.5 and 3 Watts/m² due to reduction in energy radiated into space by Earth. About 40 percent of observed sea level rise is due simply to the expansion of water as oceans have taken up this additional heat, equivalent to an energy deposit of about 3.4 billion Hiroshima scale atomic bombs over the past 25 years.

CO₂ abundances will persist with only about a 40 percent falloff over a millennium, even if we turned off Greenhouse gas production today, and given the heat input already due to increased CO₂ atmospheric concentration, sea levels will rise by at least 0.4–1m by 2100 independent of planned global reduction of fossil fuel burning.

These predictions are solid, and data on observed temperature, increased sea level rise, and ice sheet melting in the Arctic and Antarctic all are consistent with fundamental theoretical expectations.

Going further than these generic predictions requires detailed models of the atmosphere, clouds, pollution, and ocean currents, as well as more detailed time series measurements throughout Earth. No one doubts that this is very difficult, or that there are uncertainties that dominate the specific longer-term predictions. As an outsider, it is difficult to critically assess the details.

Dr. Koonin has devoted significant time to examining the results of climate modelers, but he has not been directly involved in the modeling. All other things being equal, one might choose to rely on the assessments of the community of thousands of climate scientists who have spent their lives improving modeling relevant physical processes, and who openly present their data and models, warts and all, for critical peer review. Their goal is not to reach a desired outcome, but rather to make accurate predictions. The greatest scientific accolades usually go to those who disprove conventional wisdom, so that the pressure to “conform” that is often publicly assumed when scientific consensus is discussed is often illusory.

Residual uncertainties do not invalidate the basic picture, any more than our existing uncertainties about dark matter in cosmology invalidate the basic Big Bang model, or whether the inability to yet numerically model much of detailed nuclear physics using the underlying Strong Interaction theory suggests that that theory is not the correct theory of the interactions between quarks in protons and neutrons.

The difference is that the uncertainties in these fields, in spite of their intrinsic importance for understanding our origins, have little immediate or urgent relevance for global public policy. But climate science does.

It is here that we should celebrate the uncertainties in climate science, openly acknowledged and described by the community of climate scientists and the IPCC. The fact that IPCC models allow as little as 2⁰C of heating or as much as 5⁰C by century’s end, under a “business as usual” global policy without significant reduction in fossil fuel consumption, means that there is some hope of “manageable” climate change impacts in this century, if we prepare to deal with them.

But the fact that the uncertainties also allow for extreme warming and disruption should also give us pause. I am reminded of the phrase used by Clint Eastwood in his Dirty Harry movies, when pointing his potentially empty gun at a suspect, he asks, “You’ve got to ask yourself a question: ‘do I feel lucky?’”

Or in a more scientific vein, of Pascal’s famous wager, where he argued that a belief in God hedged one’s bets, even if God didn’t exist. If we respond to climate concerns by developing new sustainable energy production methods that doesn’t destabilize our global economy, what is the downside of doing so, even if some of the stated concerns may turn out to be overestimated?

Climate science is not different than other science. It may be much more complicated than cosmology or particle physics, but it progresses by the same rules. Like the rest of science, uncertainties remain, and the forefront is always unsettled, but these facts should neither stop us from pushing on, nor provide a justification for inaction when the consequences of inaction could be severe.