by Judith Curry

In the end, the so-called scientific consensus on global warming doesn’t look like much like consensus when scientists are struggling to explain the intricacies of the earth’s climate system, or uttering the word “uncertainty” with striking regularity. – Nate Cohn

The New Republic (TNR) has an interesting article on the pause entitled Global Warming Hiatus: Where Did the Heat Go? As per the Wikipedia:

Domestically, TNR as of 2011 supports a largely modern liberal stance on fiscal and social issues, according to editor Franklin Foer, who stated that it “invented the modern usage of the term ‘liberal‘, and it’s one of our historical legacies and obligations to be involved in the ongoing debate over what exactly liberalism means and stands for.”



Excerpts from the article:

If scientific models can’t project the last 15 years, what does that mean for their projections of the next 100?

It might seem like a decade-long warming plateau would cause a crisis for climate science. It hasn’t. Gerald Meehl, a Senior Scientist at the National Center for Atmospheric Research, has seen hiatus periods before. They “occur pretty commonly in the observed records,” and there are climate models showing “a hiatus as long as 15 years.”

JC comment: I would certainly like to see some clarification on Meehl’s statement. AGW refers to warming since about 1900. The previous ‘hiatus’ is the period 1940-1976. Climate models don’t simulate the 1940-1976 period very well. And if the current hiatus extends well beyond 15 years, what does that say about the climate models?

But all this leaves a big question, one that scientists have been trying to answer: If the atmosphere is warming more slowly than projected, where did the heat go?

There are two ways to create a global-warming hiatus: The heat can go somewhere other than the atmosphere, or there might be less heat in the climate system than scientists predicted.

Global warming estimates usually center on measures of air temperature. But the climate system also can move heat from the atmosphere to somewhere else, like melting ice.

The most obvious culprit is the ocean, which absorbs 90 percent of the heat added to the climate system. With the oceans holding so much heat, the focus on mean surface temperature as the measure of global warming misses much of the point. Minor shifts between the oceans and the air could keep the planet heating up, even while slowing the pace of atmospheric warming. And that wouldn’t necessarily be good news, since warmer oceans would raise sea levels, change the climate, and hurt the ocean’s ecosystem.

JC comment: Exactly how does focusing on the mean surface temperature miss the point? Global warming is pretty much defined in context of the mean surface temperature. People live on the surface, not in the ocean below 700 m. Yes, warming the ocean interior will cause some sea level rise associated with thermal expansion. But this line of argument that warming in the deep ocean will change the climate (presumably due to changes in the ocean circulation) really just supports the argument for ocean circulations being a primary driver for climate (the natural variability hypothesis promoted by many skeptics).

But other scientists think that the heat is missing because it never made into Earth’s climate system. The idea that heat might not have made it relates to the concept of “forcing.” The term refers to the forces that add or remove heat from the climate system. The best known example of forcing is the Greenhouse effect, where greenhouse gases in the atmosphere trap heat that might otherwise radiate into space. But there’s negative forcing, too—i.e., other pollutants that reflect energy back into space.

The sun itself is a major factor in forcing. Over an average of eleven years, the sun’s energy output ebbs and wanes, subtly influencing earth’s climate. The last solar maximum was in 2000, but a prolonged solar minimum has kept the sun even dimmer than usual. According to Kevin Trenberth of the Center for Climate and Atmospheric Research, lower levels of solar radiation account for 10 to 15 percent of the hiatus.

JC comment: This is the first I have heard from an IPCC author acknowledging that solar radiation has accounted for 10-15% of the hiatus. Has anyone seen a reference on this?

Explaining the rest is more difficult. Susan Solomon, an MIT professor best known for research on the ozone hole, has focused on stratospheric water vapor and aerosols. Water vapor is a greenhouse gas, and satellite data shows stratospheric water vapor decreasing since 2000—meaning less heat is getting trapped.

What all of these discoveries hint at is that scientists, at long last, have developed a better understanding of year-to-year climate variations. In a way, you could think of it like the stock market. Watching Wall Street, we see the indices rise and fall, and we know the news that has influenced the swings. Watching annual temperatures, scientists could see the fluctuations but, until recently, knew little about the news–even though they were confident that increased carbon dioxide would ensure a bull market over the longer run.

JC comment: The Wall Street analogy is an interesting one

Piecing together the hiatus puzzle—the competing effects of the oceans, stratospheric water vapor and aerosols, and sunlight on the global climate system—is difficult. Scientists want an exact account of earth’s energy budget or balance, or how much energy enters the earth’s atmosphere from the sun, how much is absorbed by the oceans and atmosphere, and how much is radiates back into space.

All of which leads to very different estimates of how much heat is getting trapped in the Earth’s climate system. Using computer models, Trenberth estimates that the earth’s net-energy balance is about 50 percent larger than James Hansen, a prominent ex-NASA scientist who relies on Argo data.

The difference matters: If the Earth’s energy balance was actually a third lower than the computer models suggest, it would mean rethinking assumptions of climate science, such as whether aerosols are reflecting even more heat out into space than previously imagined. But Trenberth thinks the problem is Hansen’s data, not the climate science. Argo misses key things—the top ten meters of oceans and the seas around Indonesia, among other “huge patches.” After accounting for those differences, Trenberth thinks that his estimate “lines-up pretty well with the values from the ocean data.” Hansen says most of the difference is due to the solar cycle, as his analysis assumed the solar minimum, while Trenberth’s estimate is for the entire decade. Adjusting for the difference reduces the difference from 50 percent to 20 percent.

JC comment: I hadn’t previously come across this disagreement between Trenberth and Hansen on the ocean heat. There are certainly problems with the Argo data, but without seeing the arguments from Trenberth and Hansen in detail (does anyone know of the relevant references?) it seems that Hansen’s argument based on data would be more convincing than Trenberth’s estimate based on ‘climate science.’

Meanwhile, Trenberth’s model doesn’t directly account for changes in stratospheric water vapor or aerosols from small volcanoes, since those “effects should be included in the CERES top-of-atmosphere measurements.” Whether his approach accounts for these subtle changes in forcing depends on just “how good the CERES values are.” Solomon approaches the problem from the opposite perspective. She emphasizes that the role of volcanoes is “unambiguous,” supported by “great” satellite measurements, and multiple sources of data. As a result, she argues that stratospheric water vapor might cover roughly “20 percent of the hiatus” along with “30 percent from volcanoes”—the oceans, and whatever else, must cover the outstanding 50 percent.

Nonetheless, the combination of imperfect data, overlapping explanations, and continued uncertainty mean that scientists cannot discount the possibility that they have overestimated the climate’s “sensitivity” to additional greenhouse gas emissions. For Herd, the last 10 to 15 years “make it more plausible that the size of climate response to greenhouse gas increase is on the lower side of what models have been projecting over the last 10 or 20 years rather than over the high side.” Herd is not alone.

JC question: Who is Herd, does anyone know? He is the most cited person in this article. Perhaps Isaac Held, a typo?

In the end, the so-called scientific consensus on global warming doesn’t look like much like consensus when scientists are struggling to explain the intricacies of the earth’s climate system, or uttering the word “uncertainty” with striking regularity. Nowhere is there more uncertainty than in the clouds.

In the current political climate, debates about things like climate change are carried out in broad-brush assertions. The challenge for scientists is that the more they understand the climate system, the more complex it gets, and the harder it gets to model with precision—not to mention making the kinds of sweeping statements the news cycle requires.

JC comment: Carrying out a debate on a complex problem such as climate change in ‘broad-brush assertions’ pretty much sums up the problem with the public debate on AGW. Using the word ‘uncertainty’ and acknowledging the existence of disagreement and debate, such as this article does, is good journalism. I guess the news cycle is somehow incompatible with good journalism?

Public doubts about climate change are already increasing, even as scientists warn that the window for forestalling dangerous warming is closing. According to Pew Research, just 45 percent of Americans believe that scientists agree that warming is mostly because of human activities, down from 59 percent in 2006. The recent wave of news and magazine articles about scientists struggling to explain the warming slowdown could prolong or deepen the public’s skepticism.

But the “consensus” never extended to the intricacies of the climate system, just the core belief that additional greenhouse gas emissions would warm the planet.

JC comment: Hmmm. . . this is an interesting redefinition of the climate change consensus, that would leave only the Skydragons outside of the consensus.

“I don’t see how you can argue against it,” Solomon observed after declaring that “carbon dioxide will be king over the long run.” Over the twentieth century, the atmosphere warmed by two degrees Celsius. That’s no small amount and there “has to be a source, if you believe in basic thermodynamics.” Skeptics point to internal variations—the natural shifts that scientists have struggled to explain over the last decade. But oceanic heat content has also been increasing, ruling out the possibility that atmospheric warming is due to internal variability. To Herd, that’s “pretty much a smoking gun.”

JC comment: Fact check, where did 2C increase over the 20th century come from? Is anyone else having trouble with the logic of Herd’s statement: But oceanic heat content has also been increasing, ruling out the possibility that atmospheric warming is due to internal variability.

The last decade is proof of climate change, not a cause for reflexive skepticism. It was the warmest on record, despite a laundry-list of mitigating factors like prolonged La Nina, a wave of modest volcanic eruptions, and an ebb in solar activity. As those attenuating factors subside, climate scientists anticipate another round of rapid warming.

JC comment: The article lost me on this last paragraph. Why are all of these mitigating factors dismissed as mitigating factors? These are important controls on global climate; the debate is whether CO2 dominates these natural factors in determining our climate. In the near term, natural variability is obviously dominating.

JC summary

I find this article significant for several reasons. TNR is a bastion of liberal journalism; in this context this article is at least as significant as the recent Economist article.

While apparently no skeptics were interviewed for the article (at least there were no quotes), there is plenty of disagreement among the mainstream climate scientists interviewed (most of whom play or have played important roles in the IPCC).

This article reinforces my characterization of the debate in this recent post Sociology of the pause:

The public debate about the pause is being conducted primarily in the MSM, op-eds, congressional testimony, and yes the blogosphere. Few journal articles have been published that explicitly tackle the pause; in any event the publication cycle occurs much more slowly than the public debate.