Posts Tagged ‘future’

Past, present and future temperatures

February 2, 2011

Check out these two graphs of past, present and future climate change:

They both provide a compelling visual picture of potential future warming in the context of past temperatures.

I wanted to use one of these graphs for a climate presentation recently, and there are pro’s and cons to each. Most importantly (to me):

– The bottom figure includes the “constant composition” scenario (C3 in yellow), which I find a useless distraction. It has no realistic value, as it implies an abrupt and arbitrary CO2 emission reduction, but continued aerosol emissions. (Aerosol particles have a short atmospheric residence time, so emissions have to be sustained in order to keep the concentration constant. OTOH, CO2 has a very long lifetime and with roughly 70% lower emissions its concentration would remain constant). It shows the amount of unrealized warming, but it most definitely is not an (even remotely) plausible scenario, and thus should not be presented as such.

– As for the proxy temperatures going back to the Middle Ages (or even further), I prefer the (mini) spaghetti graph of the lower figure over the top figure, which features only the Mann et al (2008) reconstruction.

Steve Easterbrook reminded me of my dilemma with his post comparing the top figure with one on which the bottom figure is based. He notes a few other differences:

– Different scenario’s are used in each (e.g. the top fig includes the “fossil intensive” A1FI (sort of business as usual) scenario, whereas the bottom fig doesn’t. A2 is worst case shown in the bottom graph, whereas it’s the middle of the road in the top graph.)

– Different temperature baseline (pre-industrial versus 1995-2004 period)

The top figure is from the Copenhagen Diagnosis; the bottom figure from Chapman and Davis (2010).

I chose to show the top graph, mainly because of the bothersome inclusion of the C3 “scenario” in the other one.

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What does population have to do with climate change?

August 23, 2010

Population may not be the driving force behind many of the global world problems, but it’s certainly important: Basically, it is a multiplication factor for the environmental impact of certain actions. E.g. better environmental performance of some products has occasionally been offset by its much greater use (cf. population density). Of course, if a real innovation comes along, the environmental impact could be cut more drastically (which also happens, but counting on it may be risky).

Population

The 20-80 story puts population in perspective: 20% of the world population uses approximately 80% of the worlds’ resources (dependent on the resource of course). That alone means that focusing on population isn’t where the shoe pinches in many cases: It’s the (over-)consumption in the rich areas that causes the most strain on the world’s resources.

GDP

On the other hand, I’ve understood that the reason that native cultures had relatively little impact on their environment is to a large extent due to their small population density. Burning a small piece of forest to use the land for food production may not be a great problem for the ecosystem if it only occurs sporadically, thereby not causing more disruption than the ecosystem can handle. It only becomes a problem when the magnitude increases above sustainable levels, which is intricately linked to population. There are plenty of examples in nature where too large numbers of a certain species causes stress on the ecosystem.

The Kaya identity shows that population is a multiplication factor, just as consumption is:

CO2 emission = population * GDP/capita * energy/GDP * CO2 emission/energy.

It would require a systemic analysis to see which factors are most responsible for a given problem, but it’s pretty clear that population is a factor that influences the total pressure on the system. The 80-20 ratio described above shows that consumption patterns by the rich cause the most strain on the world’s resources. I’d wager that the difference in consumption patterns between different parts of the world is (a lot) larger than the spread in population density, which would make the former most important. Population is not a factor that is easily or quickly influenced, but for the long term, it should be seriously considered as an important factor (especially because it has so much inertia).

Pointing fingers solely to, or firmly away from population, both misses the mark imho. reality is not black and white.

Greenhouse gases

How many people the earth can sustain of course depends on the other factors in the various Kaya identities: If everyone were to have the consumption pattern of an average American, we would already have overshot the long term carrying capacity of the earth. If we all live a Buddhist lifestyle, we could probably do with a few more people. It’s a trade off, as always.

Don’t want to use (and pay for) sustainable energy (cf consumption pattern)? Then use less energy (cf population).

Don’t want to use less energy? Then use (and pay for) sustainable energy.

Don’t want to do either? Go find another planet.

This leads to a major moral dilemma: Developing nations also want to increase their material welfare, but them doing so by mimicking our current ways of production and consumption is a recipe for disaster. OTOH, we have no more moral right to the earth’s riches as they do. Something has to give, obviously.

See also this thought provoking article by Michael Tobis, where he takes on the other, even bigger taboo: economic growth. Bottom line:

A given economic growth rate can be sustainable only if the average impact per unit wealth declines at an equal or greater rate.

I.e. if the carbon and energy intensities decrease at least as fast as the GDP increases.

Attempting to reach equitable economic prosperity and allowing for normally projected increases in GPD and population, Tobis estimates that the impact per unit of wealth has to decrease roughly 50 fold by 2050.

(Figures from Newman. Post based on a comment of mine over at Kloor’s blog)



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