Image from the journal Science
The forces of denialism would have you believe that the recent plateau in global atmospheric temperature disproves the theory of anthropogenic global warming. Never mind that last month was the warmest March on record, or that these events have happened in the past only to be followed by dramatic warming.
This phenomenon may give fodder to the paid shills of the fossil fuel industry, but it also gives scientists an opportunity to enhance our understanding of the climate system. It turns out that measurements of sea surface and atmospheric temperatures do not explain observed sea level rise:
In recent years, heat has actually been flowing out of the ocean and into the air. This is a feature of the weather phenomenon known as El Nino. So it is indeed possible the air has warmed but the ocean has not. But it's also possible that something more mysterious is going on.
That becomes clear when you consider what's happening to global sea level. Sea level rises when the oceans get warm because warmer water expands. This accounts for about half of global sea level rise. So with the oceans not warming, you would expect to see less sea level rise. Instead, sea level has risen about half an inch in the past four years. That's a lot.
Willis says some of this water is apparently coming from a recent increase in the melting rate of glaciers in Greenland and Antarctica.
"But in fact there's a little bit of a mystery. We can't account for all of the sea level increase we've seen over the last three or four years," he says.
One possibility is that the sea has, in fact, warmed and expanded — and scientists are somehow misinterpreting the data from the diving buoys.
But if the aquatic robots are actually telling the right story, that raises a new question: Where is the extra heat all going?
A recent study addresses this question:
Either the satellite observations are incorrect, says Trenberth, or, more likely, large amounts of heat are penetrating to regions that are not adequately measured, such as the deepest parts of the oceans. Compounding the problem, Earth's surface temperatures have largely leveled off in recent years. Yet melting glaciers and Arctic sea ice, along with rising sea levels, indicate that heat is continuing to have profound effects on the planet.
The earth's oceans have an incredible thermal mass. Much of the excess heat that is trapped by greenhouse gasses ends up in the water. Sadly, we currently lack the sensors to measure its temperature all the way down:
Much of the missing heat may be in the ocean. Some heat increase can be detected between depths of 3,000 and 6,500 feet (about 1,000 to 2,000 meters), but more heat may be deeper still beyond the reach of ocean sensors.
The conclusion? Not very optimistic:
"The heat will come back to haunt us sooner or later," says NCAR scientist Kevin Trenberth, the lead author. "The reprieve we've had from warming temperatures in the last few years will not continue. It is critical to track the build-up of energy in our climate system so we can understand what is happening and predict our future climate."
Update via FishOutofWater in the comments
Apparently the bottom water is warming, according to this draft paper. From FishOutofWater's diary:
Deep (1000–4000 m) warming of waters mostly of Antarctic origin south of the Sub-Antarctic Front of the Antarctic Circumpolar Current adds 0.065 (±0.063) W m–2. The warming below 4000 m produces a 0.047 (±0.020) mm yr–1 increase in global average sea level and the deep warming south of the Sub-Antarctic Front adds another 0.087 (±0.083) mm yr–1.
If the prospect of resumed warming wasn't bad enough, the transfer of heat to deep water is having another impact:
The dependence of deep-sea communities on surface water production has raised important questions about how climate change will affect carbon cycling and deep-ocean ecosystem function. Recently, unprecedented time-series studies conducted over the past two decades in the North Pacific and the North Atlantic at >4,000-m depth have revealed unexpectedly large changes in deep-ocean ecosystems significantly correlated to climate-driven changes in the surface ocean that can impact the global carbon cycle. Climate-driven variation affects oceanic communities from surface waters to the much-overlooked deep sea and will have impacts on the global carbon cycle. Data from these two widely separated areas of the deep ocean provide compelling evidence that changes in climate can readily influence deep-sea processes.
Not only does deep-ocean heating disturb ecosystems and the carbon cycle, it also plays a role in ocean circulation and severe weather:
Storm intensity has increased significantly since the 1980s and economic damages from storms have also escalated. Increases in coastal populations, rising real estate values and greater insurance penetration have all played significant roles; along with more and more intense storms and anomalies of multiple types. Recent research finds a strong association between the increasing severity of storms and warming of the oceans (Emanuel 2005; Webster et al. 2005; Hoyos et al. 2006). Emanuel points to the increase in SSTs and in the deep ocean to explain the increase in storm destructiveness (a function of peak winds and storm duration); Webster et al. found that category 4 and 5 storms had nearly doubled since 1950 as ocean temperatures warmed; while Hoyos et al. (2006) reached the conclusion that increased ocean temperatures far outweighed all other factors in explaining the observed increased intensity of storms.
Skeptics want us to wait until 'all the science is in' before we act, as if they could ever be satisfied. We already have a mountain of science that points to anthropogenic emission of greenhouse gasses as a major cause of global warming. While researchers continue to further our understanding of the climate system, we already have enough information to warrant drastic action to reduce carbon dioxide emissions.
Let your Senator know that they should be listening to scientists, not shills, when passing climate legislation.