I recently noted that there are reasons to think that the effects of human caused climate change are coming on faster than previously expected. Since I wrote that (in late January) even more evidence has come along, so I thought it was time for an update.
First a bit of perspective. Scientists have known for a very long time that the proportion of greenhouse gasses in the Earth’s atmosphere controls (along with other factors) overall surface and upper ocean heat balance. In particular, is has been understood that the release of fossil Carbon (in coal and petroleum) as CO2 would likely warm the Earth and change climate. The basic physics to understand and predict this have been in place for much longer than the vast majority of global warming that has actually happened. Unfortunately, a number of factors have slowed down the policy response, and the acceptance of this basic science by non scientists.
A very small factor, often cited by climate contrarians, is the consideration mainly during the 1960s and 1970s, that the Earth goes through major climate swings including the onset of ice ages, so we have to worry about both cooling and warming. This possibility was obviated around the time it was being discussed, though people then may not have fully realized it at the time, because as atmospheric CO2 concentrations increased beyond about 300ppm, from the pre-industrial average of around 250–280ppm (it is now at 400ppm), the possibility of a new Ice Age diminished to about zero. Another factor mitigating against urgency is the fact that the Earth’s surface temperatures have undergone a handful of “pauses” as the surface temperature has marched generally upwards. I’m not talking about the “Faux Pause” said to have happened during the last two decades, but earlier pauses, including one around the 1940s that was probably just a natural down swing that happened when there was not enough warming to swamp it. A second pause, shorter, happened after the eruption of Mount Pinatubo, in 1991.
Prior to recent anthropogenic global warming, the Earth’s surface temperature has squiggled up and down do to natural variability. Some of these squiggles were, at least reionally large enough to get names, such as the “Medieval Warm Period” (properly called the “Medieval Climate Anomaly”) and the “Little Ice Age.” When the planet’s temperature started going distinctly up at the beginning of the 20th century, these natural ups and downs, some larger and some smaller, caused by a number of different factors, eventually became imposed on a stronger upward signal. So, when we have a “downward” swing caused by natural variation, it is manifest not so much as a true downturn in surface temperatures, but rather, less of an upward swing. Since about a year and a half ago, we have seen very steady warming suggesting that a recent attenuation in how much temperatures go up is reversing. Most informed climate scientists expect 2015 and even 2016 to be years with many very warm months globally. So, the second factor (the first being the concern over the ice age as possibly) is natural variation in the Earth’s surface temperature. To reiterate, early natural swings in the surface temperature may have legitimately caused some scientists to wonder about how much greenhouse gas pollution changes things, but later natural variations have not; Scientists know that this natural variation is superimposed on an impressive long term upward increase in temperature of the Earth’s surface and the upper ocean. Which brings us to the third major factor delaying both non-scientists’ acceptance of the realities of global warming, and dangerous policy inaction: Denialism.
The recent relative attenuation of increase in surface temperatures, likely soon to be over, was not thought of by scientists as disproving climate models or suggesting a stoppage of warming. But it was claimed by those denying the science as evidence that global warming is not real and that the climate scientists have it all wrong. That is only one form of denialism, which also includes the idea that yes, warming is happening, but does not matter, or yes, it matters, but we can’t do anything about it, or yes, we could do something about it, but the Chinese will not act (there is little evidence of that by the way, they are acting) so we’re screwed anyway. Etc.
The slowdown in global warming is not real, but a decades-long slowdown in addressing global warming at the individual, corporate or business, and governmental levels is very real, and very meaningful. There is no doubt that had we started to act aggressively, say, back in the 1980s when any major hurdles for overall understanding of the reality of global warming were overcome, that we would be way ahead of where we are now in the effort to keep the Carbon in the ground by using clean energy. The precipitous drop we’ve seen in photovoltaic costs, increases in battery efficiency and drop in cost, the deployment of wind turbines, and so on, would have had a different history than they have in fact had, and almost certainly all of this would have occurred faster. Over the last 30 or 40 years we have spent considerable effort building new sources of energy, most of which have used fossil Carbon. If even half of that effort was spent on increasing efficiency and developing non fossil Carbon sources, we would not have reached an atmospheric concentration of CO2 of 400ppm in 2015. The effects of greenhouse gas pollution would be less today and we would not be heading so quickly towards certain disaster. Shame on the denialists for causing this to happen.
I should mention a fourth cause of inappropriate rejection of the science of climate change. This is actually an indirect effect of climate change itself. You all know about the Inhofe Snowball. A US Senator actually carried a snowball into the senate chamber, a snowball he said he made outside where there has been an atypical snowfall in Washington DC, and held it aloft as evidence that the scientists had it all wrong, and that global warming is a hoax. Over the last few years, we have seen a climatological pattern in the US which has kept winter snows away from the mountains of California, contributing significantly to a major drought there. The same climatological phenomenon has brought unusual winter storms to states along the Eastern Seaboard that usually get less snow (such as major snow storms in Atlanta two winters ago) and persistent unseasonal cold to the northeastern part of the US. This change in pattern is due to a shift in the behavior of the Polar jet stream, which in turn is almost certainly caused by anomalous very warm water in parts of the Pacific and the extreme amplification of anomalous warm conditions in the Arctic, relative to the rest of the planet. (The jury is still out as to the exact process, but no serious climate scientists working on this scientific problem, as far as I know, doubts it is an effect of greenhouse gas pollution). This blob of cold air resting over the seat of power of one of the more influential governments in the world fuels the absurd but apparently effective anti-science pro-fossil fuel activism among so many of our current elected officials.
Climate Sensitivity Is Not Low
The concept of “Climate Sensitivity” is embodied in two formulations that each address the same basic question: given an increase in CO2 in the atmosphere, how much will the Earth’s surface and upper ocean temperatures increase? The issue is more complex than I’ll address here, but here is the simple version. Often, “Climate sensitivity” is the amount of warming that will result from a doubling of atmospheric CO2 from pre-industrial levels. That increase in temperature would take a while to happen because of the way climate works. On a different planet, equilibrium would be reached faster or slower. Historically, the range of climate sensitivity values has run from as low as about 1.5 degrees C up to 6 degrees C.
The difficulty in estimating climate sensitivity is in the feedbacks, such as ice melt, changes in water vapor, etc. For the most part, feedbacks will increase temperature. Without feedbacks, climate sensitivity would be about 1.2 degrees C, but the feedbacks are strong, the climate system is complex, and the math is a bit higher level.
As time goes by, our understanding of climate sensitivity has become more refined, and it is probably true that most climate scientists who study this would settle on 3 degrees C as the best estimate, but with wide range around that. The lower end of the range, however, is not as great as the larger end of the range, and the upper end of the range probably has what is called a “fat tail.” This would mean that while 3 degrees C is the best guess, the probability of it being way higher, like 4 or 5, is perhaps one in ten. (This all depends on which model or scientist you query.) The point here is that while it might be 3, there is a non-trivial chance (one in ten is not small for an extreme event) that it would be a value that would be really bad for us.
There have been a few recent studies using what’s called an “energy balance model” approach, combining simple climate models with recent observational data, concluding that climate sensitivity is on the low end of IPCC estimates. However, subsequent research has identified some potentially serious flaws in this approach.
These types of studies have nevertheless been the focus of disproportionate attention. For example, in recent testimony before the US House of Representatives Committee on Science, Space and Technology, contrarian climate scientist Judith Curry said,
Recent data and research supports the importance of natural climate variability and calls into question the conclusion that humans are the dominant cause of recent climate change: … Reduced estimates of the sensitivity of climate to carbon dioxide
Curry referenced just one paper (using the energy balance model approach) to support that argument – the very definition of single study syndrome …
…As Andrew Dessler told me,
There certainly is some evidence that climate sensitivity may be below 2°C. But if you look at all of the evidence, it’s hard to reconcile with such a low climate sensitivity. I think our best estimate is still around 3°C for doubled CO2.
So there is not new information suggesting a higher climate sensitivity, or a quicker realization of it, but there is a continuation of the consensus that the value is not low, despite efforts by so called luke-warmists or denialists to throw cold water on this hot topic.
Important Carbon Sink May Be Limited.
A study just out in Nature Geoscience suggests that one of the possible factors that may mitigate against global warming, the terrestrial sink, is limited in its ability to do so. The idea here is that as CO2 increases some biological activities at the Earth’s Surface increase and store some of the carbon in solid form as biomass. Essentially, the CO2 acts as plant fertilizer, and some of that Carbon is trapped in the detritus of that system, or in living tissue. This recent study suggests that this sink is smaller than previously suspected.
Terrestrial carbon storage is dependent on the availability of nitrogen for plant growth… Widespread phosphorus limitation in terrestrial ecosystems may also strongly regulate the global carbon cycle… Here we use global state-of-the-art coupled carbon–climate model projections of terrestrial net primary productivity and carbon storage from 1860–2100; estimates of annual new nutrient inputs from deposition, nitrogen fixation, and weathering; and estimates of carbon allocation and stoichiometry to evaluate how simulated CO2 fertilization effects could be constrained by nutrient availability. We find that the nutrients required for the projected increases in net primary productivity greatly exceed estimated nutrient supply rates, suggesting that projected productivity increases may be unrealistically high. … We conclude that potential effects of nutrient limitation must be considered in estimates of the terrestrial carbon sink strength through the twenty-first century.
Related, the Amazon carbon sink is also showing long term decline in its effectiveness.
From Andy Skuce writing at Skeptical Science:
We have good reason to be concerned about the potential for nasty climate feedbacks from thawing permafrost in the Arctic….research bring good news or bad? [From recent work on this topic we may conclude that] although the permafrost feedback is unlikely to cause abrupt climate change in the near future, the feedback is going to make climate change worse over the second half of this century and beyond. The emissions quantities are still uncertain, but the central estimate would be like adding an additional country with the unmitigated emissions the current size of the United States’ for at least the rest of the century. This will not cause a climate catastrophe by itself, but it will make preventing dangerous climate change that much more difficult. As if it wasn’t hard enough already.
Expect More Extreme Weather
Michael D. Lemonick at Climate Central writes:
disasters were happening long before humans started pumping heat-trapping greenhouse gases into the atmosphere, but global warming has tipped the odds in their favor. A devastating heat wave like the one that killed 35,000 people in Europe in 2003, for example, is now more than 10 times more likely than it used to be…. But that’s just a single event in a single place, which doesn’t say much about the world as a whole. A new analysis in Nature Climate Change, however, takes a much broader view. About 18 percent of heavy precipitation events worldwide and 75 percent of hot temperature extremes — defined as events that come only once in every thousand days, on average — can already be attributed to human activity, says the study. And as the world continues to warm, the frequency of those events is expected to double by 2100.
Melting Glaciers Are Melting
This topic would require an entire blog post in itself. I’ll give just an overview here. Over the last year or so, scientists have realized that more of the Antarctic glaciers are melting more than previously thought, and a few big chunks of ice have actually floated away or become less stable. There is more fresh water flowing from glacial melt into the Gulf of Alaska than previously thought. Related to this, as well as changes in currents and increasing sea temperatures, sea level rise is sparking sharply.
The Shifting Climate
I mentioned earlier that the general upward trend of surface temperature has a certain amount of natural variation superimposed over it. Recent work strongly suggests that a multi-decade long variation, an up and down squiggle, which has been mostly in the down phase over recent years, is about to turn into an upward squiggle. This is a pretty convincing study that underscored the currently observed month by month warming, which has been going on for over a year now. It is not clear that the current acceleration in warming is the beginning of this long term change … that will be known only after a few years has gone by. But it is important to remember that nothing new has to happen, no new scientific finding has to occur, for us to understand right now that the upward march of global surface temperatures is going to be greater on average than the last decade or so has suggested. We have been warming all along, but lately much of that warming has been in the oceans. Expect surface temperatures to catch up soon.