Open Mind

Slow and Steady, Fast and Furious

February 1st, 2007 · 3 Comments

Since about 1975, earth has been heating up at a rate of about 0.018oC/year. Frankly, that’s not much in a single year. In fact we can’t really measure the global average temperature that accurately.

But over many years, the heating adds up. In a decade, it’s about 0.18oC, and we can measure that. Still, it doesn’t seem like much — slightly less than half a degree Fahrenheit. But in ecological terms it can have important consequences. Snow melts earlier, altering the water cycle; fewer insect pests die out due to winter freezing; glaciers begin to melt worldwide; plant and animal species slowly migrate poleward.

Another decade, another 0.18 deg.C. The timing of snowmelt runoff is now out of sync with biological cycles; glacier melting has accelerated; opportunistic species invade higher latitudes and higher altitudes; some areas experience drought while others suffer floods; the intensity of tropical storms edges ever so slightly higher.

Another decade, another 0.18 degrees. The severity of tropical storms is now noticeably increased. Glaciers, some very famous, are actually near disappearing. A heat wave in Europe kills 30,000. Ice shelves the size of Rhode Island break off the Antarctic peninsula.

Global warmth is here: what we’ve experienced already is having visible, and in some cases alarming, impacts. More to the point, global warming will continue. For the next couple of decades at least, we can expect more warming at about 0.02oC/year; by 2030, that’ll be another 0.4oC in addition to what we’ve already seen. It stands to reason that the warming we’ll experience in the next two decades will have considerably more visible, and more alarming, consequences.

From a geologic perspective, the notable thing about modern global warming is that it isn’t slow and steady. There have been bigger temperature changes in the past, in fact during a deglaciation (the transition from glacial to interglacial conditions), the global average temperature changes by about 5oC. But that typically takes 5000 years! So the sustained rate is around 0.001oC/year. The rate of modern warming is 18 times higher. In fact the planet is expected to warm by at least 2oC in the next century, and that rate, on the geologic timescale, is fast and furious. It’s no wonder that climate scientists, and environmentalists in general, are worried about the health of the planet’s living systems.

And that doesn’t even take into account the possibility that the global climate system will undergo some unexpected disruption. In fact that’s the source of some of the discord surrounding the imminent release of one part of the upcoming “Fourth Assessment Report” of the Intergovernmental Panel on Climate Change. I’ve heard two objections that the IPCC report doesn’t raise sufficient alarms about unexpected possibilities.

One of those potential nasty surprises involves the climate sensitivity. That’s the long-term change in global average temperature due to a doubling of CO2 concentration (a feat we, as a species, are destined to accomplish). The IPCC report has no surprises in its estimation that climate sensitivity is probably in the range 1.5 to 4.5oC, with a likely value around 3oC. But some research has indicated that there’s a distinct possibility the climate sensitivity is greater than the IPCC range; some estimates get as high as 10oC (which, if true, would be not an inconvenient truth but an utter disaster). The chance of such extreme sensitivity seems to be low, estimates range from 2% likelihood to 10%.

The other objection is that the IPCC report gives too little attention to the possibility of considerably greater rise in sea level. One of the confounding factors is accelerated melting of the Greenland ice sheet. Also, recent research show just how quickly ice sheets can disintegrate, often mechanically rather than thermodynamically. IPCC is said to suggest 0.09 to 0.88 meters sea level rise by 2100, but other experts suggest it is more likely 0.5 to 1.4 meters.

Meanwhile, the chief Bush administration response seems to be emphasizing geoengineering solutions, like reflectors in space to deflect solar energy, or injecting aerosols into the atmosphere to simulate the cooling effect of volcanic eruptions. But clearly the science is not sufficiently understood to pronounce such efforts safe; the risk of unexpected consequences is too great. It is my opinion that the Bush administration’s real motive is to deflect attention and public will away from the difficult emissions reductions necessary to mitigate global warming. Such strategies deserve study, but not at the cost of avoiding emissions reductions; it’s past emissions that got us into this mess in the first place, and future emissions that will end up determining just how bad the situation really is.

Tags: Global Warming

3 responses so far ↓

  • Lab Lemming // Feb 2nd 2007 at 8:58 am

    Didn’t the same runs that gave climate sensitivity > 6C/doubling also give some negative sensitivity results, which the authors arbitrarily discarded?

    I have no problem with considering outliers, but you youtoss half of them then worry about the other half, that seems fishy.

  • cytochrome_sea // Feb 4th 2007 at 11:02 am

    LL: IIRC, a few of the dropping temperature results were included, but something close to half (I wanna say 43%?) were discarded, can’t remember the ad hoc for the discards though.
    The forcing scenario in the simulation was also physically unrealistic iirc.

  • kennebecriver // Feb 14th 2007 at 8:41 am

    Meanwhile, the chief Bush administration response seems to be emphasizing geoengineering solutions, like reflectors in space to deflect solar energy, or injecting aerosols into the atmosphere to simulate the cooling effect of volcanic eruptions.

    Like saying the solution to extinction is to preserve DNA so maybe in the future we can recreate the animals.

    Anything to avoid looking in the mirror.

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