Reducing from 44,000 to 3.700 pounds is a 92% reduction. President Obama (like most other candidates) promised and expects an 80% reduction by 2050. Thus the 92% reduction discussed here is close to mainstream. The World Wildlife Fund and others have calculated a plan to reduce UK emissions 80%, starting from a level already half as much as the US.
The present 44,000 pounds per person per year in the US is net. It includes CO2 in the products we import, excludes our exports, and gives credit for almost 4,000 pounds per person per year of reforestation.
China releases 7,000 pounds per person per year, and India releases 2,400 pounds, both on the same basis as the US, net of imports, exports and reforestation.
The UN Development Program (UNDP) estimates that limiting emissions to 1.5 trillion metric tonnes of CO2 in this century will stabilize the atmosphere and limit global warming to 2C, which they think the world can handle (2007-8 Human Development Report, pp.46-47 in chapter 1 at hdr.undp.org/en/reports/global/hdr2007-2008/chapters/). They divide the century's 1.5 trillion metric tonnes by 100 years, to give an average 15 billion tonnes of CO2 released worldwide per year, or 32 trillion pounds.
With 8.8 billion people in the world on average this century (6.9 billion in 2010, annual data are in population tab of worldpath spreadsheet), the 32 trillion pound target for CO2 would allow 3,700 pounds CO2 per person per year, if we could switch to that immediately. In the long term no country can expect to use more than the average.
UNDP estimates that the above limits will stabilize the atmosphere at 450 parts per million (ppm), and may limit the increase in average world temperature to 2C (3.6F) above pre-industrial levels. Their estimates are based on modeling done for them by the Potsdam Institute for Climate Impact Research. Their estimates only address CO2, since they say releases of other greenhouse gases are balanced by releases of aerosols (dust, etc) which cool the earth (p.199, notes 29-30, quoting International Panel on Climate Change).
The International Energy Agency's World Energy Outlook 2008 agrees that 450 ppm would provide a 2C (3.6F) increase, and says 550 ppm would provide 3C (5.4F) increase above pre-industrial levels.
World average temperature has already risen about 0.8C (1.4F) above pre-industrial levels, so a goal of 2C means 1.2C warmer than now (2.2F). (p.6 of the 4th Assessment's summary for policy makers at ipcc-wg1.unibe.ch/publications/wg1-ar4/wg1-ar4.html). The 1.4F rise already endangers species, melts glaciers, and causes more extreme weather. An additional 2.2F will have many more effects.
The atmosphere now has about 388 ppm of CO2 (rising 1 ppm every 2-3 months), and many people believe it needs to go down to 350, not up to 450. It was 280 before industrialization. The alternate target of 350 would require far lower emissions, discussed below.
All these ppm numbers are based on how many molecules of carbon dioxide are in the atmosphere per million molecules of dry air. "Dry air" means water molecules are not counted. This is also called the "dry air mole fraction" or "parts per million by volume" or ppmv. CO2 molecules are heavier (44 grams per mole) than the atmospheric average (28.97 or 28.966, mostly from N2 and O2 molecules). The current 388 ppm by volume is about 589 ppm by mass (388*44/28.97=589).
The sustainable emissions per person will drop in the future, because (a) population will grow so the annual limit is divided among more people, and (b) we continue to release CO2 at high rates, using up the century's limit, and leaving less per year for the rest of the century. These calculations depend on how fast we cut:
If the world cuts CO2 rapidly for 25 years, and stabilizes at 2,800 pounds per person per year, we will achieve the needed 3,700-pound average for the whole century, with a 3.6F rise. 2,800 is near the current level of India.
CO2 per Year per Person, Pounds
]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]] 44,000 USA
]]]]]]]]]]] 11,000 World
]]]]]]] 7,000 China
]]] 2,800 Target
]] 2,400 India
If we cut slowly over 50 years, we emit so much while we are cutting that we have to stabilize much lower at 1,800 pounds per person per year, to reach the 3,700 pound average. 1,800 is near the current level of El Salvador and Sri Lanka.
These are 94% and 96% cuts from the US level of 44,000 pounds per person per year. If the US does not cut to 2,800 pounds in 25 years, someone else has to cut deeper, or the US cooks the planet.
If we could hurry up and cut down our CO2 in 10 years, we would only have to cut to 3,300, near the level of Uruguay and Sudan. If we take 70 or more years to cut CO2, the whole world has to cut to zero, since emissions while we are cutting use up the entire century's CO2 budget.
Table of 50-, 25- and 10-year Scenarios to Cut CO2
A clear review of options to provide energy sustainably is MacKay's 2008 book, Sustainable Energy withouthotair.com/download.html It estimates that large fractions of each country will need to be covered by solar collectors, wind turbines and/or biomass crops to produce the energy we use. This expansion will change views and ecosystems, though not as badly as global warming. MacKay's book does not estimate the CO2 released to manufacture those collectors and turbines, or to clear the land for biomass crops.
YOUR OWN CLIMATE MODEL
In an interactive model at chooseclimate.org/ you can move a cross to set a target level for CO2 in the atmosphere. (In their various models, we recommend starting with the older, fully documented model.) Setting it at 450 ppm (the UNDP recommendation) makes an estimate appear on another graph showing how many billion metric tonnes of Carbon could be emitted each year, consistent with this goal. Slide the cursor around on that graph, and you can read that the graph drops from 7 billion to 2 billion tonnes over the century. This is an average of 4.5 billion tonnes of Carbon per year, which is 16 billion tonnes of CO2 per year, virtually the same as the UNDP's estimate of 15 billion.
Changing the target for the atmosphere to 350 ppm yields an estimate that emissions would have to drop to zero for a while, before stabilizing at 600 million tonnes Carbon per year, which is 2 billion tonnes CO2 per year, or 700 pounds CO2 per person per year. One sees why 350 ppm is not a popular goal, though the model predicts temperature would only rise 1.9F, instead of 3.6F above pre-industrial levels. This would still be half a degree warmer than now. (In the chart of Temperature rises, you can set the baseline year to 1750 to reflect a "pre-industrial" baseline.)
SOLUTIONS are discussed on another page
REASONS FOR OPTIMISM are discussed on another page
The fruits of success will include more food, coral and species saved; fewer floods, droughts and tropical diseases; and less extreme weather.
The International Union for Conservation of Nature, which for decades has monitored the risk of species becoming endangered (the "Red List") says climate change endangers 35% of the 10,000 bird species studied, 52% of the 6,000 amphibian species studied and 72% of the 800 coral species studied (Species Susceptibility to Climate Change Impacts IUCN 2008). These species are affected by:
* desynchronization of migrations;
* uncoupling of parasite/host, predator/prey, & mutualisms (eg. pollinators);
* interaction with new pathogens and invasives;
* loss of habitat;
* increased stress;
* changes in fecundity, sex ratios and competitive ability;
* inability to deposit calcium (e.g. shells and bones).