Climate Change Made Simple

We promised we’d look at climate scenarios this week, so here you go, forty climate scenarios from the Intergovernmental Panel on Climate Change‘s 2000 Emissions Scenario Report.  Note that this graph is nearly ten years old and doesn’t include the effects of land clearance and ecosystem change, but it gives you a sense of the complexity of scenario development.

OK, let’s update and simplify these forty green house gas emission scenarios, by bunching them into four groups, and transforming that into the bottom line: average global temperature from the latest IPCC synthesis report.

The black line is historical temperature change. The magenta line imagines that we hold green house gas concentrations to year 2000 levels. You can ignore that.  The blue line assumes we undergo a “sustainability transformation” in which we hold population to nine billion, cooperate globally, and go all out on renewable energy and conservation.  It’s essentially the agreed-upon target from the Copenhagen conference.  Result: a two degree C rise in temperature, which would be manageable.  The green line is an optimistic version of “market world:” business as usual, with incentives for renewable energy, results in a robust global economy, with developing nations getting in on the act.  The red line is fortress world. It’s every nation for itself – drill baby, drill.  As the scenarios above are from 2007, some climate scientists would raise each scenario a degree or two. Note the confidence interval bars to the right.

Here’s yet another take. Using assumptions from IPCC scenarios, simply entered all the non-binding “pledges” from nations at the COP 15 conference this month to estimate that world green house gas emissions would peak at 60 gigatons CO2 around the year 2040.  This pushes CO2 levels well past 500 ppm, and raises global temperatures to 3.5 degrees (plus or minus a degree) above year 2000 levels.

Which scenario do you think is most likely? 350 ppm (uh, we’re at already at 390, so…) and minimal climate change? Over 550 ppm and a very different world?  Or somewhere in between? Probably depends on whether you’re an optimist or a pessimist.  And what does this mean for different regions of the world, like the Pacific Northwest?  More on that next week.


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