Thursday, May 2, 2013

Temperatures may be flat – but there’s no free lunch

The most commonly used measurement of global warming is the Global Annual Mean Surface Air Temperature Change (see graph at right and note below). When you read about “rising temperatures,” this is the number they’re talking about. If you look closely at the far right of the graph you can see that this temperature measurement, after shooting up for the previous couple of decades, leveled off over the last 10 years or so. This despite the fact that we’re still pumping out prodigious amounts of greenhouse gasses.
Several attempts have been made to explain this very short-term pattern in such a way as to show we might be out of the woods on global warming, mainly by weakening the “sensitivity” of our climate models. Hey – those sensitivity factors were inferred from a lot of real data covering centuries and millennia – it makes no sense to me to start fiddling with them based on 10 years worth. I don’t believe in free lunches.
In fact, the recent (and very short by ecosystem timeframes) leveling of the mean global air temperature is likely a case of borrowing from Peter now, only to have to pay Paul back later. I like this explanation because (a) it makes sense, and (b) doesn’t involve a free lunch.
According to a paper in the American Geophysical Union's Geophysical Research Letters, the reason the air temps aren't rising is that the global warming energy has gone into heating the deeper ocean waters. Normally, that doesn't happen - the surface water's warm first and since warm water floats over cold water, the deeper ocean is slow to heat. But - enter the Pacific Decadal Oscillation (PDO), which during the past decade has been pushing colder water up from the depths, and circulating the warm water down. With the cold water on top, the ocean has been absorbing more of the heat energy of global warming, leaving the surface air temperatures unchanged.
Trouble is, when the next PDO cycle starts, that pattern will reverse, and much of that absorbed energy will re-enter the atmosphere, and we'll pay for this decade of "flat" temperatures with a decade of rapidly increasing temperatures. In fact, say the scientists, this is exactly what happened in the late 80s and 90s (1998 remaining one of the hottest years on record).
That's the trouble with looking at one number (mean global surface temperature) as a proxy for the complex phenomenon of climate change. We have to remember that “Global Warming” refers to the entire 3D globe, not just the surface.
We're coasting now, but hang on to your hat!

Note 1: The graph from NOAA (see the original at Temperatures are shown as a departure (“anomaly”) from the 1951-1980 average. So over the last 10 years or so, the mean surface temperature has been holding steady at 0.6 degrees Celsius (1.08 degrees Fahrenheit) over the 1951-1980 average.

Saturday, March 30, 2013

Great video: 62 years of global warming in 13 seconds

This video has been out there for a bit, but bears watching again (hey, it's only 13 seconds). Here's my new take-away. Notice how the warming pattern has fluctuated wildly over the years (weather, natural variations). But, what really leaped out at me this time is how obvious the long term trend is.

Saturday, March 9, 2013

Global Warming - The Big Picture

Many thanks to David Roberts at Grist for this one. See my post (11/27/12) about the World Bank report - hitting 4 degrees Celcius would seem to be likely even if all carbon reducing commitments are met! (And, given the record, how likely is that?)

Friday, February 22, 2013

Permafrost melting – do we care yet?

A recent paper in the journal Science by Anton Baks et. al. has studied the effects of past climate warming on the planet’s permafrost and concluded that a 1.5˚C  global rise in  temperatures over the long term baseline will create a significant weakening of the permafrost. We’re already halfway there (0.8˚C) and will hit that target by mid-century.

Permafrost cracking pattern in the high Arctic.
Photo credit: Brocken Inaglory via Wikimedia Commons
When the permafrost melts, the buried plant matter is exposed to sunlight (UV rays in particular), the the process of bacteria converting that stored carbon to CO2 and methane accelerates, releasing perhaps 40% of these greenhouse gases into the atmosphere. That can’t be good, no matter what.

Just how bad it is, however, is still scientifically uncertain, as is the rate of warming up there.

On “just how bad it is,” there are mitigating factors. One, the bacteria convert a lot of the biomass to CO2 which is much less threatening than methane. No one knows what that ration will be, but the scary articles usually assume its all methane. Not so. Two, the process takes time – decades will pass between the arrival of the warming and the actual increase in atmospheric heat trapped as a result. By that time, the total greenhouse gas releases from all the usual suspects may drown out the permafrost contribution.

On the rate of change front, however, there is plenty of reason to worry. Studies by NASA in 2012 indicate that the permafrost is melting much faster than the global average – in fact, they’ve already risen by 2.2-3.9 degrees C (or 4-7 degrees F) over the last century. Another study shows that the actual recorded rises in methane and CO2 over the world’s permafrost is much, much greater than predictions by the IPCC and others. One thing we’re certainly learned from three decades or so of climate predictions is: the consensus is always low, and often very low, compared to what actually shows up.

We need more study on the permafrost front, certainly. My takeaway is this: it’s one more time bomb ready to go off, and when you add up all the similarly under-studied and under-reported time bombs (melting of the glaciers comes to mind), we need to be very, very worried. Even if the odds are low, it’s the only planet we have and we can’t afford to guess wrong.