In a campaign event last week, Republican presidential frontrunner Jeb Bush exhibited Stage 2 climate denial, saying (video available here),

Look, first of all, the climate is changing. I don’t think the science is clear what percentage is man-made and what percentage is natural. It’s convoluted. And for the people to say the science is decided on, this is just really arrogant, to be honest with you. It’s this intellectual arrogance that now you can’t even have a conversation about it.

The Politics



Unfortunately, denial of human-caused global warming may be a prerequisite for any viable Republican presidential candidate. Conservative and Tea Party Republicans are the one group of American voters among whom Stage 2 climate denial is the majority position, but they’re also the group that most reliably votes in GOP primary elections.



In American politics, a candidate first has to win a primary election before reaching the national ballot. For Republicans, that means appealing to conservatives. It’s not clear that a Republican presidential candidate can accept climate science and run a viable primary campaign.



The Science



Nevertheless, the scientific evidence supporting human-caused global warming is just as strong as the evidence linking smoking and lung cancer. Last year, the IPCC stated with 95% confidence that humans are the main cause of the global warming that’s occurred since 1950. Their best estimate is that we’re responsible for about 100% of the warming during the past six decades.

Gavin Schmidt, Director of the NASA Goddard Institute for Space Studies, put together this graph showing what’s known as the probability density function of the human contribution to global warming since 1950, based on the IPCC report.

The probability density function for the fraction of warming attributable to human activity (derived from Fig. 10.5 in IPCC AR5). The bulk of the probability is far to the right of the “50%” line, and the peak is around 110%. Created by Gavin Schmidt.

As the figure shows, natural factors have most likely caused a slight cooling since 1950, meaning that human factors are most likely responsible for all the warming we’ve seen and then some (110%). The odds that natural factors are responsible for the majority of global warming over the past six decades is virtually zero.

This assessment is based on multiple lines of evidence. There are climate model simulations, which can’t account for the observed warming without a dominant influence from the increased greenhouse effect. There are “fingerprints” of human-caused global warming, which are effects we expect to see in the patterns of climate change if those changes are due to the increased greenhouse effect. I explain some of these in one of my Denial101x lectures.

Denial101x lecture 3.4.3 by Dana Nuccitelli.

Basic physics is perhaps the most convincing piece of evidence behind human-caused global warming. Long-term global warming and cooling events are caused by changes in the Earth’s energy balance. If there’s more incoming than outgoing energy, the planet warms, and vice-versa. Natural variability, like ocean cycles, only causes short-term temperature changes.

Since 1950, the Earth has had a large and growing energy imbalance due almost entirely to the human-caused increased greenhouse effect. There’s actually been a slight decrease in incoming energy from the sun during that time, an hence a slight solar cooling effect.



Overall, the energy imbalance (a.k.a. radiative forcing) from the increased greenhouse effect has caused more warming than we’ve observed, having been offset by some cooling from other human pollutants (aerosols) blocking sunlight, as shown in this figure from the IPCC report.



Assessed likely ranges (whiskers) and their mid-points (bars) for warming trends over the 1951–2010 period from well-mixed greenhouse gases (GHG), other anthropogenic forcings (OA; including the cooling effect of aerosols and the effect of land use change), combined anthropogenic forcings (ANT), natural forcings (NAT), and natural internal climate variability. The observed surface temperature change is shown in black, with the 5 to 95% uncertainty range due to observational uncertainty. Source: IPCC AR5 Figure 10.5.

And of course because of these many lines of overwhelming evidence, there’s a 97% consensus among climate scientists and in their peer-reviewed climate research on human-caused global warming. There are a few outlier climate scientists who disagree, like Judith Curry, who incorrectly claimed “Jeb gets it exactly right,” but these contrarians are a slim minority.



As the evidence clearly shows, Jeb got it exactly wrong. It’s not arrogant to accept the overwhelming preponderance of scientific evidence, basic physics, or a 97% expert consensus; rather, it’s ignorant to deny it.



The Policies

At the same campaign event, Bush ironically claimed,



I think, as conservatives, we should embrace innovation, embrace technology, embrace science; it’s the source of a lot more solutions than any government-imposed idea.

Yes, the conservative presidential frontrunner suggested that conservatives should embrace science just a few moments after he rejected the science on global warming. Nevertheless, a candidate’s favored policies are more important than his acceptance or rejection of science. Unfortunately, while Bush suggested that conservatives embrace technology, he only specifically supported natural gas,



We’ve had a decrease [in carbon emissions], a pretty significant decrease and it will continue on, not because of Barack Obama, but because of the energy revolution, because of free-enterprise, because of private property rights because of American innovation has created a combination of two existing technologies: hydraulic fracking and horizontal drilling has created an explosion of lower carbon energy that is being used to replace higher carbon energy.

Research has shown that at best, natural gas can only act as a (short) bridge fuel during the transition to low-carbon energy sources if we want to avoid dangerous global warming, and in fact it might not even be a suitable bridge. In any case, “we should embrace innovation, embrace technology” is not a concrete policy platform.



Bush clearly opposes the legally-mandated government regulations of carbon pollution enacted by the Obama administration. However, it’s the Democratic Party that’s supported free-market carbon pricing policy alternatives, even offering small-government revenue-neutral compromise legislation. While the Republican Party and the fossil fuel industry have tried to repeal the government regulations, they haven’t accepted that compromise offer or proposed any alternative policies of their own.

Bush also tried to pass the buck, claiming that other countries are responsible for solving the problem,

we need to encourage the (nations) states that have had an increase in carbon emissions, We’re not one of them!

It’s true that the USA has seen a modest decline in its carbon pollution in recent years. However, claiming that other countries are now responsible for solving the problem is like a 400 lb. man who loses 10 lbs. claiming that 250 lb. men are now responsible for solving America’s epidemic of obesity. It’s especially irresponsible given that Jeb Bush hails from Florida, which has at least $145 bn in property value lying less than 1 meter above the high-tide line, with sea level likely to rise by about 1 meter by the end of the century if we continue with the status quo.



Although it’s moving in the right direction, thanks in large part to the Obama Administration’s efforts to tackle the problem, the USA is still one of the world’s largest carbon polluters in terms of both total and per capita emissions. That won’t change until the Republican Party stops denying science and starts taking the problem seriously.

