Numbers and scale

Lately I've been trying to get a better sense of overall scale so that I can fit numbers into it when I hear them. I'm trying to put together sets of numbers for reference. These may be of interest to others.


Emissions
(Source: EPA, http://www.epa.gov/climatechange/emissions/globalghg.html; IPCC 2007, http://www.ipcc.ch/publications_and_data/ar4/syr/en/figure-spm-3.html)

• Total global GHG emissions: ~around 30 Gigatons of CO2 (GtCO2/yr) (current); ~49 Gigatons of CO2 equivalents (GtCO2e/yr) (2004)
• Global GHG emissions in 1990, the Kyoto Protocol's index year: ~22 GtCO2/yr; ~39 GtCO2e/yr
• US emissions: ~7 GtCO2/yr
• Average US power plant's yearly greenhouse gas emissions: ~1 million metric tons of CO2 equivalents

(Note the difference between CO2 and CO2 equivalents.)

Other Greenhouse Gases:
Some other greenhouse gases, with global warming potential as a multiple of carbon dioxide (source: EPA, http://www.epa.gov/oms/climate/420f05002.htm; IPCC 2007, http://www.ipcc.ch/publications_and_data/ar4/syr/en/figure-spm-3.html):

• CO2 - 1
• Methane (CH4) - 21
• Nitrous oxide (N2O) - 310
• Hydrofluorocarbon (HFC)-134a - 1,300

These are emitted in smaller quantities than CO2 (CO2 makes up around 77% of greenhouse gas emissions when figured as CO2e), which is why you don't hear way more about them. But they ARE important. I've heard some people argue that we should be focusing more on methane than on CO2 right now, because it's effect occurs faster; and I've read that the single most effective international action taken versus climate change was in fact the Montreal Protocol controlling ozone-depleting substances (most of which are also potent GHGs).

Temperature
(Source: EPA, http://www.epa.gov/climatechange/downloads/Climate_Basics.pdf)

• How much we've warmed over the past century: 1.3 degrees F
• How much further we're on track to warm no matter what: about 1 degree F
• Current international consensus on the threshold of warming we want to avoid going past: 2 degrees C (roughly 3.6 degrees F)
• Likely average temperature rise by 2100 under business as usual scenarios: 3 to 7 degrees F (but note that emissions have lately been rising at worst-case scenario rates, so the higher value is considered more likely than the lower)

Money
The fact is, it's highly disputed how much climate change mitigation will cost. I've heard "2% of GDP" thrown around a lot as an expected cost of climate change mitigation. But there are those who would argue that that's too low, and those who would argue it's too high, and both arguments have some merit. Here I'm just going to give some representative numbers to give a sense of scale (source: Global Warming Gridlock, Victor 2011):

• What the EU thinks developing countries will need to be given to help them carry out climate change mitigation: $100B per year.
• What China estimated it would need to be given to help it carry out climate change mitigation: over $400B.
• What an MIT team estimated the developing world would need to be paid to cut world emissions in half by 2050: $400B to $3T per year, rising from 2020 to 2050.
• Rough amount of money channeled to developing countries over the lifetime of the Kyoto's Protocol (not per year) via the Protocol's Clean Development Mechanism, the current largest international funding source: $50B

For adaptation, things are in my opinion even shakier to estimate, because it depends on how bad the situation you're adapting to is, and there are tipping points whose arrival are hard to predict. However, to give a sense of scale, a recent estimate by the EPA's sea-level experts found that it would cost about $1 trillion in direct costs to fortify the contiguous US against a three-foot sea level rise.

How Much Can the West Do On Its Own?

A lot of developing countries take the position that right now, the burden of cutting emissions should be taken on by the developed countries, while developing countries continue to develop on business as usual (BAU) curves or with moderate controls that slow but don't stop their emissions growth. Is this workable?

I'm not sure I fully understand this yet, but here's my first shot at it. The IPCC 2007 report contains a set of scenarios that assume different GHG projections and the expected warming associated with them: http://www.ipcc.ch/publications_and_data/ar4/syr/en/figure-spm-5.html. If I'm reading this correctly, the B1 scenario keeps warming to around 2 degrees C, which is considered mostly "safe." In this scenario, emissions are assumed to rise to around 56 GtCO2e/yr by 2030 and 58 GtCO2e/yr in 2040, and decline fairly sharply thereafter.

So, to figure this out, you need projections of the developing world's business as usual emissions trajectory and how much room (if any) that curve leaves underneath the B1 scenario - that's how much developed countries would have to reduce their collective emissions to to do it all on their own. I'm obviously not the first person to have thought of this. Here's a study that suggests it simply doesn't leave enough for developed countries to get down to under any realistic scenario (note that I've just skimmed this.) They figure China's emissions alone at between 11 and 19 GtCO2e/yr by 2030, with the total developing world at between 23 and 37 GtCO2e/yr (the paper uses carbon equivalents rather than CO2 equivalents; the conversion factor is 1 Ce to 44/12 CO2e). They use what looks to me like a more stringent emissions reduction curve than the IPCC B1 scenario, though. In the immortal words of Barbie, modeling is hard; let's go shopping.