Climate Change: It’s Real, and It’s Us

Bad Astronomy
The entire universe in blog form
Sept. 30 2013 8:00 AM

Climate Change: It’s Real, and It’s Us

Earth on fire

Photo by peasap on Flickr/NASA/Phil Plait

Climate change is real. The Earth is warming up.

Moreover, by implication and by fact: Climate change deniers are wrong.

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In the very first highlighted conclusion on the very first page of the report, the authors come out swinging:

Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.

Emphasis mine. Still, that’s the major fact to walk away with. The biggest change over previous reports is how confident scientists are that humans are behind global warming. We’ve known about the effects, and now we can be quite sure that our own emissions are behind it.

Politically, this may be the most important part. People like James Inhofe (R-Okla.) can spew ridiculous assertions and continue to live in a fantasy world, but this part of the IPCC report is specifically written for policymakers. The increased certainty over previous reports is what they need to understand.

Still, the ramifications of climate change need to be driven home.

The report has many. In fact, right after that opening salvo they go on to say that each of the last three decades has been warmer than the last, and all three have been warmer than any other decade since 1850.

This is critical to understand, so here’s the plot showing land and ocean surface temperatures, averaged over a decade:

Land and sea surface temperatures averaged over ten year periods.
Land and sea surface temperatures averaged over ten year periods.

IPCC report

As you can see, the last three decades have been warmer than any before, and the 2000-2009 decade warmer by far.

Averaging over a decade is a good way to show this because temperatures change quite a bit year-to-year, and climate change only starts to show itself after a sufficiently long period of time. If you look on shorter time scales, you might think things are warming faster or slower than they really are.

This is the major fallacy recently promoted by the climate change deniers: That the warming has “stalled” over the past decade or so. That’s simply not true. Temperatures have flattened, but to say the global warming itself has stopped is dead wrong. I’m not splitting hairs, either, because the distinction is critical. Here’s the difference:

1) We’re talking surface temperatures here, which is not the best way to represent the extra energy the Earth has absorbed from the Sun. Climate change happens because the amount of heat absorbed by the Earth from the Sun is not balanced by the amount the Earth radiates away into space. Give off too much and the Earth cools; keep too much and it heats up. Greenhouse gases in essence trap heat, so the more carbon dioxide we put into the air, the less heat the Earth can shed, and we warm up.

Right now, that extra energy is getting transported into the deeper ocean. We know this is happening. And the ocean is a much, much bigger reservoir of heat than the air is —it can store and transfer far larger amounts of heat than air (that’s why a sauna set to 80° C will be relaxing, but a hot tub set that high will quickly kill you). As the IPCC report notes, ocean temperatures are rising.

2) The flattening of the surface temperatures lately is nothing new. Despite deniers beating the drums about it, we’ve had such “pauses” before. Here’s the other part of the temperature showing annual land and ocean surface temperatures (this is the same graph as above, but not averaged over whole decades):

Land and sea surface temperatures on an annual basis.
Land and sea surface temperatures on an annual basis.

IPCC report

Let me ask you, and answer honestly: What’s the very first thing you notice about that plot? It’s obviously the steep rise in temperatures since about 1900. But note that there have been several times the slope of that rise has changed. From 1940 – 1960 it was fairly flat as well (you can see that in the decadal average, too). But then it took off again, shooting back up. It also rose steeply from 1900 to 1940 or so after a period of mild cooling.

The point is, the trend over time is up. Natural variations can cause cooling — ocean absorption of heat, volcanic explosions, aerosols sent into the air by humans — but those are at best small variations on the much larger trend. And that trend is hot.

So no matter how much the denial machine froths and fumes at this latest so-called “pause”, the graph makes it very clear that all of this has happened before, and will happen again. But to think this means climate change has “stopped” is simply foolish, and anyone trying to make that argument is clearly wrong.

There is far more to the IPCC report than just temperature, of course. Other big conclusions:

·      Precipitation rates are changing; dry places are getting drier, and wet places wetter;

·      Arctic sea ice is declining (despite, again, the ridiculous claims of the deniers);

·      Upper ocean heat content is rising;

·      Sea levels are rising (over a 150 millimeters —five inches — in the past century);

·      The oceans are getting more acidic (caused by CO2 absorption);

·      Atmospheric carbon dioxide levels are rising, as are methane and nitrous oxide levels, and are higher now than they have been in 800,000 years.

co2_mm_mlo_lrg
Annual amount of atmospheric carbon dioxide (in parts per million), measured at Mauna Loa.

Graph by NOAA Earth System Research Laboratory

That last one is the key to this whole thing. We have been dumping all three of these greenhouse gases into the atmosphere at a rate of billions of tons per year for the past century, and that’s upset the natural balance of the planet.

We’re heating up, and it’s our damn fault.

And there’s more: Obviously, if we do nothing, just go about business as usual, things will continue to get worse. But even if we improve, cut back on CO2 emission, things will still continue to get worse for quite some time. [Note: The IPCC report on mitigation techniques — that is, what we can do about all this — is due out in April 2014.]

This is the new normal. Hotter temperatures, more extreme weather, loss of ice at the poles. Ocean acidification is scary, too; that’s already affecting corals, causing die-offs, and can have negative impacts on the entire food chain in the oceans.

There’s more, a lot more. That’s the important stuff, though. Still, I strongly urge you to read the report itself. Also, reliable sources have been writing about this since the report came out Friday. Here are a few good links:

·      Climate scientist Michael Mann writing for The Guardian

·      Skeptical Science, as always, has an excellent summary, noting that another big conclusion to draw from the IPCC report is how much more confident they are that this is due to human influence

·      Seth Borenstein at Common Sense Canadian

·      NASA’s Earth Observatory site          

·      An article written by two climate change professionals at The Conversation

·      Real Climate, also as usual, has a great writeup

There are plenty more, but that’s enough to give you the gist.

Of course, the deniers have been spinning at nearly relativistic speeds trying to downplay this report. They talk about the pause, they talk about how sensitive the climate is to CO2, they talk about the IPCC being unreliable. But the bottom line is they’re wrong. Ironically, due to its very nature, the IPCC is actually quite conservative; the panel has actually been getting flak from real scientists because the observations — heat absorption, ice loss, sea level rise, and so on — have in almost all cases actually outpaced predictions from earlier reports. In reality, things are worse.

So there you go. I know a lot of people will be saying I’m being alarmist, but you know what? I’m being a realist. Climate change is alarming.

And if someone denies that, denies the facts, denies the conclusions of thousands of actual climate scientists, denies the evidence, denies that CO2 is a greenhouse gas, and denies that there’s even a problem, well, what does that make them?

I’d much rather know the alarming truth than be in constant denial while things get worse all around me.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

[Correction (Sept. 30, 2013): I initially wrote that sea level rise was 150 cm, or five feet, in the past century. It's actually 150 millimeters, or five inches. I sincerely apologize for that; a typo in my draft got carried through when I converted metric to  imperial units. Obviously, a sea level rise of five feet would be massively catastrophic...I'll note that the IPCC report says that by 2100 the likely rise in sea level will be about a half meter, or 18 inches, which in itself is pretty bad.]

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