Wednesday, August 20, 2014

The Heat is On (still) — and here's how scientists know it is

The following short essay was published this May in the Summer issue of The Aquarian. I've revised and adapted it for this blog, with many more hyperlinks and graphics. 

A Cold Winter in a (Still) Warming World

When you look at the big picture, there's been no “pause” in global warming

By Syd Baumel

It was Winnipeg's coldest winter since 1898. Throughout most of North America, the deep freeze broke records, made headlines and (inevitably) provided fodder for global warming doubters, deniers and disinformers.

So where did the global warming go this winter? Answer: nowhere.

While we were freezing like it's 1898, across the Atlantic Europe was enjoying one of its warmest winters on record. Witness those not-so-wintry Olympics in Sochi.

Even here in North America, it was an unusually warm winter out west – the warmest on record in California where the heat was so parching that by April the state was fully engulfed by drought. Up the road a piece, Alaska basked in its eighth warmest winter ever.

But, as the proverb goes, when a whole bunch of blind men examine an elephant, a tusk, a trunk and a big floppy ear at a time, it can lead to a comically distorted picture of the whole.

Every month, the National Oceanic and Atmospheric Administration (NOAA) of the United States – a global authority on weather and climate – analyzes data from around the world and publishes a “state of the climate” report. While we were freezing this winter, it turns out the planet as a whole never even shivered.

Remember November? With hindsight, it was a sign of things to come as a chilly autumn month segued abruptly into winter, with over a week left to go. Globally? According to NOAA, it was pretty hot that month, record hot:

The combined average temperature over global land and ocean surfaces for November 2013,” NOAA reported in December, “was record highest for the 134-year period of record, at 0.78°C (1.40°F) above the 20th century average of 12.9°C (55.2°F).”

Of course, it wasn't until December that the cold wave unmistakably swept across most of Canada and the U.S. (Ironically, some climate scientists hypothesize it was a quirky side effect of global warming, the result of a sagging polar vortex meeting a shuffling jet stream.) So what about them apples, NOAA?

NOAA: “The average combined global land and ocean surface temperature for December 2013 was the third highest for December since records began in 1880, at 0.64°C (1.15°F) above the 20th century average of 12.2°C (54.0°F).”

And on it went.

January: “... fourth warmest on record.”

February: “... the 21st highest for February on record.” (That's warmer than five out of six of those Februaries.)

As for March, the month when winter threatened to take up permanent residence in these parts, the big picture was thoroughly unintimidating: “the combined average temperature over global land and ocean surfaces for March rebounded and was the fourth highest on record.”

As I write this early in May after a (still) unseasonably cold April, NOAA's monthly report isn't out yet, but don't expect any surprises. The last time the world experienced a month that was cooler than the 20th century average for that month, many of you weren't even born yet. The rest of us didn't know an MP3 from a B52, and the number one “record album” that month was by a saucy new sexpot named Madonna: Like A Virgin. It was February 1985. Statistically, that kind of warm streak is like flipping heads 350 times in a row. The odds against it happening by chance are so high they make a quadrillion look like small change. (Update, August 18: True to form, April continued the global warming streak. In fact, it tied with 2010 for the warmest April on record. May didn't tie; it set a new record. So did June. July took a breather. It was only “the fourth highest on record." Update, December 13: The heat continues. August, September and October each set a new heat record for their respective months. Indeed, The first ten months of 2014 were the warmest such period on record,” says NOAA, and “The most recent 12-month period, November 2013–October 2014, broke the record (set just last month) for the all-time warmest 12-month period in the 135-year period of record...”)

Pausing to ponder “the pause”

Something similar has been happening with the recent so-called “pause” in global warming. Even though virtually every year since 1997 has been warmer than any year before 1997 (probably going back thousands of years), the slope of the warming trend has slowed down and pretty much plateaued since about 2002. Here's what it looks like: 

In the context of the longest instrumental (i.e., measured with thermometers) temperature record in the world (source: the Hadley Climate Research Unit of the UK's Met Office), the “pause” looks like a speed bump, at best. Other temperature records show the same pattern. 

It should be noted, though, that recently, when researchers more accurately accounted for Arctic warming, the pause more or less disappeared from the temperature record (for a straightforward explanation of their research, watch this this excellent video by one of the two scientists)

When the Hadley surface temperature record (“HADCRUT4”) is adjusted to include missing polar and other geographic data by using the satellite temperature record, which began in 1979, the recent pause all but disappears. (Chart created with 
Still, if we stick to the half dozen or so land- and satellite-based datasets in their current configurations, there has been no statistically significant warming since the mid-1990s (in statistics, “significant” means the odds are at least 20 to 1 that the warming trend is real, not a random uptick). Deniers and disinformers have glommed onto this as proof that we're no longer warming (if we ever were) despite the continuing proliferation of human-generated greenhouse gas emissions – the only credible cause for modern day warming. 

(And now, a very brief digression – feel free to skip ahead.) Why are human greenhouse gas emissions “the only credible cause for modern day warming”? The answer (which isn't brief) can be found in any authoritative source on climate change. Still, much as an infographic can be worth a thousand words, so can a balance sheet of all the known human and natural warming and cooling forces – “radiative forcings,” as climate scientists say – since before the industrial revolution. The one below is from the latest report by the supremely authoritative Intergovernmental Panel on Climate Change (the IPCC). 

The IPCC's most recent balance sheet of natural and anthropogenic (human caused) cooling and warming influences (“forcings”) on the planet's climate leaves little room for doubt that anything other than anthropogenic forcings can account for the precipitous warming we've seen in modern times. Source and discussion here, starting on page 53. 

(End of digression.)

But just as a cold winter in North America can distract us from the big picture of a warm winter worldwide, a stalled warming trend in the air above us can distract us from the fact that the planet as a whole has kept on accumulating heat. It's just that the heat has found some more determined customers lately: the oceans, the snow and the ice.

While air temperatures have temporarily peaked, the ocean waters that cover 70 percent of the planet, and the ice and snow in polar regions and mountain ranges, have been warming and melting with a ferocity the world has probably not seen since we emerged from the last ice age.

The oceans are the greatest heat sink on the planet. They absorb well over 90 percent of the infrared solar energy trapped near the Earth's surface by the greenhouse effect. But since 1990, these giant shock absorbers have been working overtime, soaking up atmospheric heat about five times as greedily as they were between the 1950s and 1990. If anything, that breakneck pace has increased since 2000, global warming pause be damned. Here's what that not-so-pause looks like: 

The startling rise in ocean heat content since the early 90s has yet to take a pause. SOURCE:  (slide 2, as of August 2014). 

And then there's the cryosphere, our planet's motherlode of snow and ice.

We've all heard of the astonishing ice melt in the Arctic. Since the 1950s, the summer ice that covers that frozen sea has shrunk by nearly eight percent per decade. As momentous as that is (a 50 percent decline in 60 years), the everything-must-go liquidation melt of Arctic sea ice has only accelerated since the late 1990s. Climate scientists are having to revise their estimates of when the Arctic will be ice-free in the summer from “mid-century or later” to “any decade now.”

This IPCC graph shows how multiple, independent measurements (“datasets”) are documenting a rapid and dramatic decline in the Arctic's summer sea ice (it's declining year-round, too). SOURCE: the IPCC's Fifth Assessment Report, 2013 (Figure TS.1, p. 38). 

Climate change doubters like to point out that Antarctic sea ice has been growing, so it all balances out. But the two are not equal. The modest ice expansion over the Antarctic's frigid waters has been dwarfed by the massive recession over the Arctic's. Take a look: 

The folks at use their adroit GIF-making powers to illustrate the net global sea ice loss, as documented by satellites since 1979. Story here

What it comes down do is whether we want to see the world as it is or pick and choose only those bits that confirm our biases. When it comes to the planet's massive cryosphere, the most important question we can ask is what's been happening to all of it, not just the parts that are growing here or disappearing there. The answer is it's been going fast.

It may not seem like it to us Canadians, but nearly all of the world's glacial ice – the fresh-water glaciers and ice sheets (mega-glaciers greater than 50,000 square kilometres in area) that cover land and mountains – is concentrated in Greenland and Antarctica, not Winnipeg. Late last year, the UN's Nobel prize-winning Intergovernmental Panel on Climate Change (IPCC) completed its review of the physical science that has accumulated since its last report in 2007 and brought the world up to speed. The average rate of ice loss from Antarctica, the IPCC's cryosphere scientists estimated, was a formidable 30 billion tonnes per year between 1992 and 2001. But from 2002 to 2011 – the decade when global warming appeared to take a holiday (judging by air temperatures) – Antarctica's ice loss “likely” (IPCC-speak for 66 to 100 percent probability) accelerated to 147 billion tonnes per year.

The acceleration was even more dramatic in Greenland. The IPCC's experts (leaders in their respective fields who volunteer their time to produce the IPCC reports) believe it's “very likely (90 to 100 percent probability) that ice loss there has vaulted from 34 billion tonnes per year between 1992 and 2001 to 215 billion tonnes per year during the decade of “no global warming.” (You can read the IPCC's discussion here, on pages 40–46.)

But what about all of those photogenic glaciers outside of the remote, frozen poles – on mountain ranges like the Rockies, the Andes and the Himalayas and on icy lands like Alaska and the Canadian Arctic? It turns out they've been losing ice at an even greater clip – and again, without “pause.” 

Using data from 1971 to 2009, the IPCC estimates there has been a gradual acceleration in this erosion of glacial ice outside of Greenland and Antarctica. During the entire period, it estimates the melt “very likely” averaged 226 billion tonnes per year (give or take 135 billion tonnes). But from 1993 to 2009, it probably averaged 275 billion tonnes per year. And by 2005 to 2009, the rate peaked at 301 billion tonnes per year. 

Here is what all that polar ice sheet and global glacier melt looks like, both before “the pause” (1991 to 1998) and “during” it:

Not a pause in sight: a planet losing ice. From Figure TS.3, page 41, Technical Summary, Climate Change 2013: The Physical Science Basis (IPCC), 2013. (On the right, “SLE” stands for sea level equivalent.) 

Add it all up, and in just one recent decade we've probably melted over six trillion tonnes of the ice cubes in Mother Earth's icebox. In a world that just keeps on warming, there is no Safeway or Price Choppers we can go to to put those ice cubes back. Quite the contrary. According to the IPCC's best guesstimate, a lot more melting is locked in, even if we turn off all the dirty power tomorrow: “There is high confidence that current glacier extents are out of balance with current climatic conditions, indicating that glaciers will continue to shrink in the future even without further temperature increase.” 

All of this ice melting and ocean warming has sent sea levels soaring. According to data from NOAA, global mean sea level – which had its own little pause in the early 90s – has climbed nearly three inches just since 1997 (see their graph below). To put that into perspective, the IPCC estimates that the cumulative sea level rise since 1901 is 7.5 inches. Since most of the recent spike in sea levels has occurred since 2001, nearly 40 percent of the entire sea level rise since 1901 has occurred in little over a decade – while global warming has supposedly stopped.

There has been nothing “pausey” about the planet's sea level since the late 1990s, according to the satellite record which begins in 1993. SOURCE: NOAA

Climate scientists, the IPCC and every major scientific body on the planet all seek out, see (however imperfectly) and agree on the big picture. They seek clarity, not confusion. They can tell the elephant from the tusks. Whether the air is warming less for 15 years and the ice and oceans are melting or warming more, or vice versa, when skeptical, bean-counting climate scientists balance the books, the planet is still running a fever.

The only way to prevent the climate disruption we're already seeing (for maximum climate volatility, add heat rapidly and stir) from becoming a climate disaster a generation or two from now is to stop adding coal, oil and gas to the fire – and fast.

This is what climate science's “balance sheet” of global warming since 1971 looks like, as tabulated for the IPCC's most recent report (page 264). It is truly startling to realize that warming of the lower atmosphere – of the thin layer of air above us – is represented by that wee purple curve at the bottom. Even the melting cryosphere (grey) can't hold a candle to the oceans’ capacity to absorb roughly 93% of the heat we keep adding to the climate system – and clearly to do so without any recent “pause.” 

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