The new US administration has taken its time in employing a science adviser. Back when Barack Obama was elected in 2008, science adviser John Holdren was nominated a month before inauguration. I had the honor of meeting him last December, and I've never been more intimidated or impressed by someone's sheer intellectual presence. His commanding knowledge of every conceivable aspect of physical science—hurricane physics, ecophysiology, glaciology, and aerosol chemistry—was simply awe-inspiring. It made me feel like there was little I could tell the guy that he didn't already know.

WIRED OPINION About Benjamin Sanderson (@benmsanderson) is a climate scientist at the National Center for Atmospheric Research in Boulder, Colorado.

The rumored frontrunner for the same position for the Trump administration is William Happer, a physicist from Princeton. Happer's academic science credentials are solid, but he's earned a reputation as a climate-change skeptic, with good reason. He recently told the Guardian, "There's a whole area of climate so-called science that is really more like a cult. It's like Hare Krishna or something like that. They're glassy-eyed and they chant. It will potentially harm the image of all science."

The Benefits of Carbon Dioxide

Broadly, Happer isn't a climate denialist per se, rather he's a climate change enthusiast, firmly believing that further elevated CO 2 levels would be beneficial for humanity. He also professes to care deeply about the scientific method. So, in this spirit, I'll challenge these assumptions with a mind open to his viewpoint.

Happer told ProPublica earlier this month that historical predictions had overestimated the climate change that we observe today: "What's not only shaky but almost certainly wrong is the predicted warming," he said. "In 1988, you could look at the predictions of warming that we would have today and we're way below anything Hansen predicted at that time."

Some background: Jim Hansen was one of the first scientists to run a 3-D coupled atmosphere ocean model while working at NASA in the late '80s. His 1988 paper was massively ahead of its time in its attempt to project future warming for future rising greenhouse gas concentrations. He and his co-authors considered three possible scenarios: one in which emissions increased exponentially, one in which they increased linearly, and one in which emissions were curtailed before the year 2000.

What's stunning about this paper is that it's pretty bang on. Hansen's second scenario assumed that CO 2 concentrations would continue to grow linearly. Between 1975 and 1985, carbon dioxide levels increased 15.6 ppm, and this rate has continued at about 16 ppm per decade ever since. Moreover, global mean temperatures between 2006 and 2015 were about 0.7° C warmer than the 1951-1980 mean—almost exactly what Hansen predicted.

This is particularly impressive because the computational architecture that NASA was working with in the late '80's was about 200 times less powerful than the iPhone 7. Understanding of clouds, aerosols, land surface processes, and ocean dynamics has advanced by orders of magnitude since 1988. In short, it wouldn't be surprising if we had gotten it wrong 30 years ago, but broadly, we didn't.

In the interview with ProPublica, Happer went on to assert that the climate sensitivity is "probably around 1° C, it's not 3 1/2° C or whatever the agreed-on number was. It may even be less."

The range of uncertainty for climate sensitivity—the long-term increase in global mean temperature, in Celsius, that would occur if CO 2 concentrations were instantly doubled from pre-industrial levels—has remained fairly constant for the last 40 years. Broadly, the higher the true number is, the warmer our future will be. In 1979 experts concluded this figure was between 1.5° C and 4.5° C, exactly the same bounds as stated in the 2013 report from the Intergovernmental Panel on Climate Change. If anything, since then, most studies have suggested that scientists of the '80s might have slightly underestimated how much warming we were in for.

The Challenges of Climate Detective Work

Using historical data to work out the likely value of climate sensitivity is detective work, relying on clues from ice and sediment cores in order to reconstruct past climates. But these reconstructions have big error bars. Similarly, interpreting the warming of the recent past requires separating the effects of aerosols, ocean heat uptake, and greenhouse gases. We can't use the past alone to tell us how warm the future will be. In short, Happer's confidence that climate sensitivity is 1° C or less is unscientific: We don't have enough evidence to be this confident on any value yet, and we can't rule out the high end (or the low end) of the range.

Happer has noted that throughout most of history, CO 2 levels were higher than they are now, and that is true. But it's likely that the Earth hasn't seen present-day concentrations in the last 2-4 million years. And with no action on climate change, CO 2 concentration levels will probably hit about 1,000 ppm, which would likely represent a 30-million year high.

But it is the rate of change of climate, rather than the absolute numbers, that makes adaptation difficult. If emissions continue to grow, over the course of 100 years humanity could potentially raise temperatures by as much as the previous 20,000 years, during which time humans and other species were able to slowly adapt in a changing climate.

Happer also suggested that resurrecting the high levels of carbon dioxide in Earth's deep past would be a good thing: "Nothing bad happened, in fact the earth flourished with more CO 2 … you can already see the Earth greening. If you look at agricultural yields, they're steadily going up," he told ProPublica.

This is an incomplete truth. Carbon dioxide can make plants more productive, and this effect can be detected from satellites. But if CO 2 levels continue to increase, both temperature and precipitation are likely to change, and incidences of extreme heat are likely to increase. As carbon dioxide levels rise, plants tend to close their stomata, possibly making them less able to survive the heat stress. The earth will have more arid regions in the future, making irrigation more difficult. Climate change will likely have competing positive and negative effects on plant growth, and we don't know which of these will dominate, or whether changes in agricultural technology will be able to mitigate any losses.

Scientists love nothing more than to question and shoot down each other's results. But through those arguments, over time certain conclusions emerge. In this case, the balance of evidence shows that anthropogenic climate change is likely to alter the state of our environment significantly over the coming decades and centuries, and that these effects can be reduced by curtailing our greenhouse gas emissions. Yes, there are uncertainties in the details of the projections, but no reasonable risk assessment would use this as an excuse for not taking mitigating action. If you let your 6-year-old drive you to work tomorrow, there's some chance you might both make it, but it doesn't make it a good idea to give him the keys.

Happer's potential appointment is in some ways more worrying than the administration's hires to date, such as the appointee for EPA administrator Scott Pruitt, who simply denies scientific consensus on climate, making his position easy to dismiss in rational debate. Happer's background in science and his selective consideration of the data give his opinions a veneer of respectability. If he is going to champion the principles of the scientific method and rational discourse, he must be able to defend his positions in the light of the overwhelming evidence for the significant risks associated with anthropogenic climate change. And that's a fight he can't win.