On the advent of this 40th Earth Day, nine climatologists from Germany take a look at the range of likely scenarios if we do nothing more to reduce the causes of global warming than is called for by what the world agreed to at Copenhagen last year. The bottom line:
"it is equivalent to racing towards a cliff and hoping to stop just before it."
Here's the summary, as laid out in an opinion essay in Nature (subs req'd, although with something this important, it really shouldn't be:
- Nations will probably meet only the lower ends of their emissions pledges in the absence of a binding international agreement
- Nations can bank an estimated 12 gigatonnes of Co2 equivalents surplus allowances for use after 2012
- Land-use rules are likely to result in further allowance increases of 0.5 GtCO2-eq per year
- Global emissions in 2020 could thus be up to 20% higher than today
- Current pledges mean a greater than 50% chance that warming will exceed 3Â°C by 2100
- If nations agree to halve emissions by 2050, there is still a 50% chance that warming will exceed 2Â°C and will almost certainly exceed 1.5Â°C
Those projections are based on national pledges made earlier this year in accordance with the Copenhagen Accord, which is supposed to get us on a path to keep warming at 2 °C above pre-industrial norms. "It is amazing how unambitious these pledges are," write the essay's authors. How amazing? Consider:
Our most pessimistic projection assumes that countries hit their lowest stated ambitions, take advantage of surplus allowances and use credits fully. This leaves us with potential 2020 emissions from developed countries of 19.9 GtCO2-eq -- or 6.5% above 1990 emissions.... In other words, in the worst case the Copenhagen Accord pledges could permit emission allowances to exceed our business-as-usual projections.
And on the other hand:
In a more optimistic scenario, we assume that nations meet the ambitious end of their stated pledges without using surplus allowances and land-use credits. This gives 15.7 GtCO2-eq for developed countries in 2020 -- 15.6% below 1990 levels.... Although this is significantly lower than business-as-usual, it is still far above an emissions pathway that could realistically reach the 2 °C target.
The essay also points out a potentially fatal flaw in the approach many governments assume they can take to deal with global warming. Near-term emissions are almost always allowed to increase, with steep cuts made later on. My home and native land is perhaps the worse offender in this regard:
Canada is the only country that both weakened its ambitions in the course of the negotiations, and effectively argued for an increase of 2020 emission allowances above its current Kyoto Protocol target: 3% above instead of 6% below 1990 levels.
Though the authors don't mention it, this is the sort of strategy embraced by Bjorn Lomborg, who argues that because it will be cheaper to implement technological fixes in the future, we can wait to start bringing down emissions. What Lomborg and other adherents of "discounting" ignore is that, while they are right about the general trend of declining costs of renewable energy sources, carbon capture and other techno-solutions, the magnitude of the emissions cuts required grows dramatically the longer we wait to begin making the cuts.
Discounters are gambling on the slope of the cost of technologies being steeper than the slope of the emissions cuts required to avoid catastrophic global warming. Given the massive uncertainties involved in economic predictions, that's just not reasonable. Hence the essay's conclusion: "it is equivalent to racing towards a cliff and hoping to stop just before it."
Their advice: get our act together now. Don't repeat the mistakes of Copenhagen at the new global climate change conference in Mexico this fall.