Climate Update

[marcusmarcusrc]

The summary for policymakers of the IPCC Fourth Assessment Report (the biggest climate document of the last five years, both in size and importance) was just released today.

"Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations."
Two nice graphs: pg. 16 (SPM-2): Forcing changes since 1750: Anthropogenic contributions: 0.6 to 2.4 W/m2 (uncertainty mainly due to interactions between aerosols and clouds). Change in solar forcing: 0.06 to 0.3 W/m2. pg. 18 (SPM-4): Comparing models run with "just natural" forcing and "all forcings" to observations, showing how the last half century of warming is not explained without human influences. (this is a qualitative comparison: there are of course more quantitative measures of attribution behind this)

For the most part the report attempts to put probability ranges on all the reported numbers (rather than just reporting ranges, as in the third assessment report).

Projected temperature change for the next century: 1.1 to 6.4 degrees C (without probability, since they still don't quantify probabilities for emissions scenarios) (compare to 0.6 degrees C for 1900 to 2000). Sea level rise: 18 cm to 59 cm (compare to about 17 cm for 20th century). This does not include Greenland/Antarctica, which could add another 10 to 20 cm or more, but the melting processes of these ice sheets are still poorly understood.

It is also "likely" that we will see both more droughts and more heavy precipitation events, and more intense tropical cyclones in the 21st century.

Discussion also available at realclimate.

Note that the summary is based on a report that is fully drafted but "embargoed", and will not be released until April. The science in the full report is set, and won't change, but there may be minor edits and wording changes. The summary itself still needs some editing (I've noticed a few typoes), but apparently once it was "hammered out" by scientists and politicians to be as understandable as possible while still accurately reflecting the draft chapters they wanted to release it as quickly as possible.

Note that it seems like most people think that this report has been somewhat "conservative" in its statements.



In other climate news, Prof. Lindzen of MIT appeared on Larry King along with Bill Nye the science guy. Sadly, in the short clip I watched (the first couple minutes of the show), Lindzen repeated one ridiculous skeptic canard, namely "it hasn't warmed in the past 8 years" because 1998 was as warm as any year since. Claiming that this indicates that there isn't a warming trend makes about as much sense as saying on June 8th, "hey, it was warmer on June 1st than it is today. Therefore, there isn't a warming trend! I bet it won't be any warmer in August than now!" Lindzen is probably the best scientist among the "climate skeptic" population, but this kind of statement among others is why I've lost any respect for him. It is also odd that a 4 person panel would consist of 2 "skeptics" and 2 "mainstreamers" where the skeptics are a climatologist and an economist and the mainstreamers are a weather channel host and a TV science guy - why didn't they get a mainstream scientist or economist on the show? Why did the show have to "evenly represent" two sides of view that are totally not evenly represented in the real world? etc.

Comments

[marcusmarcusrc.livejournal.com]

Honestly, I have a very hard time imagining a world with 10x the current average GDP, so it makes it difficult for me to evaluate tradeoffs accurately. My gut feeling is to be cynical and assume that much of Africa will still be dirt poor, as well as decent chunks of Latin America and SE Asia.. but I acknowledge that I could be very wrong. I do admit that with some exceptions, the poor in the US have a standard of living much higher than they would have had 100 years ago (at least, as measured by access to things/services, or health/lifespan). But if the rest of the world can really reach US/European standards of living in 100 years, which our economic models or extrapolation of average GDP growth predicts.. well... that would be something. Of course, Africa has averaged 0.19% GDP growth since 1973, compared to 1.4% for the world average... so obviously there has been historical growth discrepancies. And despite the general consensus of my colleagues and other economists, I sometimes wonder how GDP can continue to grow at such a high rate (and for example, worldwide GDP growth in the 50s and 60s was 2.9%, so is the slip from 2.9 to 1.4 a trend or a fluctuation?)(GDP #s from Maddison, 2001)

Oh. And the distribution _is_ relevant, because while the poorest people don't directly pay mitigation costs (I admit they pay some indirectly) they do suffer from climate change. In fact, poor Bangladeshis living on a flood plain are expected to suffer disproportionately from sea level rise and changes in precipitation patterns. Ditto for African subsistense farmers.

Also, the assumption that money not spent on emissions mitigation will almost automatically lead to improved standards of living for the poor - I'm also dubious. Yeah, it is standard economics of limited resources, but... I can see a lot of areas less worthwhile than climate mitigation that we could choose to shift money out of, and that in fact I feel like money we don't spend on climate mitigation is as likely go into those areas as into HIV prevention. Also, I feel like even ignoring the climate externalities, that there are a lot of economic distortions in energy production/use that lead society to use more energy resources than would be otherwise optimal... but that's again more gut instinct than hard numeric analysis.

We know that we are making significant changes to the environment with unknown impacts. When sticking long-lived chemicals into the environment, whether it be PCBs, CFCs, or GHGs, where low cost abatement measures exist we should be taking them because we _can't_ test all the possible impacts. Our best estimates of climate change involve a lot of bad but not catastrophic outcomes in the next 100 years. But there are potentials for certain tipping points (precipitation feedback loop in the amazon, melting of the greenland ice sheet) that are unlikely (well, greenland is likely on a long time scale, unlikely on less than 200 years) but would be impacts of disastrous magnitudes. If we do exceed 5 degrees celsius increase on the 100 year time scale (I'd estimate a couple percent chance) I think it is likely that that temperature increase will be accompanied by some unforeseen disastrous change because we're talking about a temperature change of the magnitude of glacial/interglacial shifts, and at extremely high rates.

And I still don't know how we value coral reefs. It is likely that they'll suffer a lot in any but the most optimistic scenarios - but how much HIV prevention is saving the coral reefs worth? Are we talking about their value as part of the larger oceanic ecoystem? Or their existence value? Or their tourism value? Or what? Is their existence worth a billion dollars? (surely it is) A trillion dollars? (I'd think so, but I don't know) A quadrillion dollars? (probably not...) Of course, even "just" a billion dollars is a lot of HIV prevention, and it is hard to say that "these coral reefs are worth hundreds of thousands of human lives" (though if loss of the coral reefs led to collapse of fisheries, then their loss might indeed lead to a loss of many thousands of lives). And a billion dollars is also less than a single stealth bomber, and I think a coral reef is worth many, many, many stealth bombers.

[kirisutogomen.livejournal.com]

Also, the assumption that money not spent on emissions mitigation will almost automatically lead to improved standards of living for the poor - I'm also dubious. Yeah, it is standard economics of limited resources, but... I can see a lot of areas less worthwhile than climate mitigation that we could choose to shift money out of, and that in fact I feel like money we don't spend on climate mitigation is as likely go into those areas as into HIV prevention.

You have to be realistic about your assumptions regarding where the money is going to come from. Sure, in a perfect world we'd shift money out of reality TV and into climate mitigation, but those are actually two very distinct decisions. Emissions abatement is in practice just going to act as a general drag on economic activity, with a bias toward energy-intensive activity. So yeah, not much is going to come out of HIV prevention, but nor do you get to pick some especially egregious expenditure and say, hey, let's take the money from there. In general, the poor participate approximately equally in economic growth, and emissions abatement has approximately proportional effect on economic growth.

Less generally, the extra impact on energy-intensive economic activity tends to disproportionately impact the people who rely on agriculture and low-tech manufacturing, i.e., the poor. Unless of course we exempt India and China from GHG reductions, in which case we're getting the worst of both plans -- lower economic growth plus global warming.

Anyway, yeah, the thought of what the world is going to look like with a $100,000 GDP per capita is pretty mind-boggling, but I seriously expect it. I also won't attempt to explain how, any more than I would have recommended to someone in 1907 to forecast what the structure of the global economy would look like over the ensuing 100 years.

What's the long-term trend rate of growth? Who the hell knows? 2.9% sounds more reasonable than 1.4% to me. Maddison's date of 1973 is kind of a breakpoint, as you know. (FWIW, GWP grew at 5.1% last year and 4.4% the year before.)

And as far as comparing coral reefs to HIV prevention and stealth bombers, I just refer back to what I started with. You can't make up a scenario where you take money from the bombers and give it to the reefs, because those are two separate decisions. If you want to value the coral reefs, you have to do so in terms of money, because that's the only reasonable metric. If you think stealth bombers aren't worth nearly as much as they cost, that's a statement about bombers, not about coral reefs.