NASA’s Hansen: “If We Stay on With Business as Usual, the Southern U.S. Will Become Almost Uninhabitable.”

Climatologist Slams Media for “Silent Summer”: Poor Coverage of Link Between Extreme Weather and Human-Caused Climate Change

The nation’s top climatologist, NASA’s James Hansen, has a new paper out — and he has been speaking out. At’s Moving Planet event in New York on Saturday, he said:

“Climate change — human-made global warming — is happening. It is already having noticeable impacts…. If we stay on with business as usual, the southern U.S. will become almost uninhabitable.”

Hard to argue with that.

The combination of extreme heat, constant Dust-Bowl conditions in the Southwest and South central, the whipsawing from drought to deluge in the Southeast, and decade after decade of sea level rise will create nearly intolerable conditions by century’s end (see “An Illustrated Guide to the Science of Global Warming Impact”). Conditions might look a lot like this:

Oops, that’s the US Drought Monitor for Texas this week! Dark red is “exceptional drought” (covering 86% of the state) — virtually no rain for a year. Red is “extreme drought” (covering 97% of the state) — a Palmer Drought Severity Index of -4 or worse.


Imagine what it will be like when much of the South is like this most of the time (other than the occasional record-smashing deluge) — and temperatures are some 9°F to 11°F warmer on average. It will be the great repopulation of the North.

Hansen also has a new paper out on climate change in which he says:

It is time for all of us to get Tea-Party-angry about what our political system has become and about the intergenerational injustice being perpetrated on young people.

Again, no argument here.

The most interesting part of the paper is his critique of the media coverage (“Silent Summer”), his discussion of the intimidation of climate scientists, and a tantalizing introduction to a forthcoming analysis on extreme weather and attribution to human emissions. Also, he doesn’t like the phrase “global weirding.” Here are the highlights:

Silent Summer

There is ample evidence of growing climate disruption. But despite record or near-record heat and drought in the United States this past summer with simultaneous extreme flooding, and despite comparable extremes in China and elsewhere, there has been little public discussion of the connection of these climate extremes with human-made climate forcing.The media are partly responsible for the silent summer, as they have mainly chosen not to examine connections between climate anomalies and human-made causes. A cynic may ask whether their silent summer is related to increasing right-wing control of media and large advertising revenues from fossil fuel companies. Regardless of reasons for media silence, should scientists be making more effort to draw public attention to the human role in climate anomalies?

Scientists face one long-standing obstacle to public communication and one new factor. The old difficulty arises from limits on our ability to detect expected change in a chaotic climate system, especially concerning the significance of specific regional events. The new factor is the likelihood of being pilloried for reporting evidence of a human role in climate change.

In a later section, he elaborates on that last sentence:

Character Assassination

There was criticism of my congressional testimony about global warming in the 1980s, but it was mainly normal healthy scientific skepticism (Kerr, 1989). A different sort of criticism, including an element of character assassination, has developed since then and has been leveled most heavily against scientists Ben Santer, Michael Mann and Phil Jones. The approach has included acquiring and digging into personal correspondences of scientists in search of any inappropriate or questionable statements, as well as fine-toothed scrutiny of their scientific analyses in search of any element, however minor, that could be criticized.

The ultimate target of the critics in Santer’s case was a specific sentence that Santer was responsible for as a lead author in the 1995 IPCC report: “Taken together, these results point towards a human influence on climate.” The target in Mann’s case was the temperature record of the past millennium, which Mann had shown to resemble a “hockey stick”, bending upward into rapid warming in the past century. The target in Jones’ case was his analysis of observations showing the rapid warming of the past century.

The important point I wish to note is that each of these three targets, the scientific conclusions that provoked the critics and which they aimed to destroy or discredit, have been shown in subsequent analyses to have been correct, indeed, dead-on-the-mark.

However, the scientific community is well aware of the toll that these attacks took on the scientists, despite the fact that their work was eventually vindicated and corroborated.

Thus, it would not be surprising if these experiences have an effect on the willingness of other scientists to make statements that draw attention to the likely role of human-made forcings as a contributor to the climate extremes of the past summer.

In any case, there is abundant evidence that the attacks on the science and the scientists have contributed to a pullback in public support for national and international efforts to find a path forward that would lead to the large reductions in emissions that are needed to stabilize climate and provide young people with a promising future.

This is important, because the actions that are required can only be achieved through the political process. That will not happen until the public understands and supports what is needed.

Finally, Hansen has an interesting discussion of extreme weather and attribution to human emissions:

Limits on Detection

Global warming is expected to intensify climate extremes: (1) Warmer air holds more water vapor, and precipitation occurs in more extreme events. ‘100-year floods’ and even ‘500- year floods’ will become more likely. Storms fueled by water vapor (latent heat), including thunderstorms, tornadoes and tropical storms, will have the potential to be stronger. Storm damage will increase because of increased flooding and stronger winds. (2) Where weather patterns create dry conditions, global warming will intensify the drought, because of increased evaporation and evapotranspiration. Thus fires will be more frequent and burn hotter.

Observations confirm that heat waves and regional drought have become more frequent and intense over the past 50 years. Rainfall in the heaviest downpours has increased about 20 percent. The destructive energy in hurricanes has increased (USGCRP, 2009).

Is the Texas drought related to human-made global warming? There is strong reason to believe that it is. Basic theory and models (Held and Soden, 2006) and empirical evidence (Seidal and Randel, 2006) indicate that the global overturning circulation, air rising in the tropics and subsiding in the subtropics, expands in latitude with global warming. Such expansion tends to make droughts more frequent and severe in the southern United States and the Mediterranean region, for example. Climate simulations, shown in Figure 3 for one of the best climate models, support that expectation.

[JR: I suspect this study underestimates likely drought in the West due to early snow melt and other factors. I’ll have to take a look.]

So the occurrence of unusual Texas heat and drought is consistent with expectations for increasing CO2. But is this year’s event just climate ‘noise’? Scientists need to help the public distinguish climate change caused by global warming from natural climate variability.

I used ‘climate dice’ in conjunction with testimony to Congress in 1988 to try to help the public understand that the human-made climate ‘signal’ must be extracted from the large ‘noise’ of natural climate variability. I believe the public can grasp the concept of natural climate variability and its effect on perceptions of climate change.

In an upcoming post (Climate Variability and Climate Change, Hansen, Sato and Ruedy) we try to clarify this matter via simple maps and graphs that show how the odds have changed, allowing comparison of expectations and reality. We believe this is a truer approach than the frequently suggested alternative of dropping the long-standing ‘global warming’ terminology in favor of anything (‘climate disruption’, ‘global weirding’, etc.) that avoids the need to explain the occurrence of unusually cold conditions.

We show that a ‘signal’ due to global warming is already rising out of the climate ‘noise’, even on regional scales. Figure 4 is an example, showing surface air temperature anomalies in the last four Northern Hemisphere summers relative to the climate of 1951–1980, the time when the ‘baby-boomers grew up — it was a time of relatively stable climate, just prior to the rapid global warming of the past three decades.

During 1951–1980 the world had equal areas of blue (cool), white (near average), and red (warm) temperature anomalies. The division 0.43σ, where σ is the local standard deviation about the local 1951–1980 mean, was chosen to yield equal area categories for a normal (‘bell curve’) distribution of temperature anomalies. The other divisions in the figure, 2σ and 3σ, allow us to see the areas that have extreme anomalies relative to climatology. The frequency of an anomaly greater than +2σ is only 2–3 percent in the period of climatology for a normal distribution. The frequency of a +3σ event is normally less than one-half of one percent of the time. The numbers on the upper right corner of each map are the percentages of the global area covered by each of the seven categories of the color bar.

Figure 4 reveals that the area with temperature anomaly greater than +2σ covers 20–40 percent of the planet in these recent years, and the area greater than +3σ is almost 10–20 percent. The United States has been relatively ‘lucky’, with the only +2–3σ areas being the Texas region in 2011 and a smaller area in the Southeast in 2010. However, these events are sufficiently fresh in people’s memories that they provide a useful measure of the practical impact of a 3σ anomaly.

There is no good reason to believe that the United States, or any other region, will continue to be so ‘lucky’. On the contrary, as shown in our upcoming post, there is a clear positive trend to increasing areas of +2–3σ anomalies, consistent with expectations for the climate response to increasing greenhouse gases. If BAU emissions continue, the area with anomalies of +2–3σ and larger will continue to increase.

The chaotic element in climate variability makes it impossible to say exactly where large anomalies will occur in a given year. However, we can say with assurance that the area and magnitude of the anomalies and their practical impact will continue to increase. Clear presentations of the data should help the public appreciate the situation as global warming continues to rise further above the level of natural variability.

However, as Mother Nature makes the dominance of human-made climate change more obvious, proponents of business-as-usual have engaged in another method to stifle communication by scientists about global warming.

Hard to argue with that!