Sometimes it's difficult to see what's most likely to happen and not the more pleasant scenario, but the Energy Information Administration (EIA) does just that in its energy outlook "reference case." Based on existing laws and policies (i.e. "business as usual"), EIA predicts that annual world carbon dioxide emissions will increase from 30.2 billion tons in 2008 to 43.2 billion tons in 2035. Roughly 278 billion tons of carbon will be pumped into the atmosphere over those 28 years  and, according to findings by the National Research Council, Earth's temperature will raise by about 0.5 degrees Celsius because of it. The laws and policies needed to stop these emissions are unfortunately not in the forecast, and it is past time to adapt for the change in climate that is coming.
It's business as usual in the policy world. The Durban climate summit is over, but little progress was made. The European Union and a few other nations committed to new emission limits, but Japan, Canada and Russia did not renew their pledges. India and China (the world's largest emitter) resisted any limits, and the United States, of course, is not a party. Kyoto "lite" is going forward with most global emissions uncapped. The summit also produced the Durban Platform for Enhanced Action in which, according to a New York Times editorial, China and India agreed to "play by the same rules as everyone else" in any future agreement. However, the practical outcome of the decision is unclear, which called on parties to develop an agreement "applicable to all Parties . . .with a view to ensuring the highest possible mitigation efforts by all Parties . . ." A poorer country could easily argue that its "highest possible mitigation effort" is less than a wealthier one. Perhaps the dynamic will change, but any effective proposed agreement is likely to encounter the same opposition that rose in Copenhagen, Cancun, and Durban, reflecting differences over sovereignty and development driven by the demands of global population increase.
The failure of international negotiations on climate policy is compounded by the complications and limitations of each available step for reducing greenhouse gas emissions. Energy efficiency could make a huge dent and save money, but moving forward requires not only a change in policy but an underlying change in culture. Nuclear energy was stalled by Three Mile Island and Chernobyl and has been stalled again by Fukushima. Sequestering carbon underground from coal-fired plants could reduce emissions substantially, but initiatives to demonstrate its efficacy and cost have made little progress to date. Adding more forests would remove carbon from the atmosphere, but the world is currently losing forests overall and efforts so far have not reversed that course. Biofuels could play a role, but critics argue they compete with food crops and require subsidies, and some biofuels, such as firewood, are unsustainably collected. Natural gas will play a larger role and produce twice the energy of coal per ton of carbon emitted, but it is still a source of atmospheric carbon.
Consider also the numbers for solar, wind and hydro energy which feature prominently in public discussions of renewable alternatives to fossil fuels. Solar energy is appealing about 10,000 times more is absorbed by the Earth then people produce but the EIA puts it at just 0.01 percent of current total world energy production and, despite rapid growth, expects it to reach only 0.08 percent by 2035. The EIA estimates current wind energy production at 0.14 percent of total world energy and forecasts that it will also grow rapidly, but only will reach 0.65 percent of total world energy by 2035. The EIA puts hydro energy at 2.11 percent of current total world energy production, but forecasts less rapid growth for it than solar or wind, and expects it to reach just 2.49 percent of total world energy production in 2035. 
It's also instructive to look at how much more global temperature would rise if solar, wind and hydro were not available at the levels estimated by EIA between 2008 and 2035 and coal were used instead. The additional rise would be about 0.0016 C in the case of solar, 0.0126 C for wind, 0.0565 C for hydro, and 0.0706 C for all three of these alternatives combined. These avoided temperature increases are significant and renewable energy installations will keep on giving beyond 2035, but they are a small component of the overall temperature equation, which by the same assumptions is predicted to rise 0.49 C from carbon added to the atmosphere over this period.
These limits to mitigation deliver a clear message: It's past time to begin adapting to climate change with the same effort and specificity that communities invest in preparing for a coming hurricane or flood. Many involved in climate policy see this, but many other policymakers do not. We need to be ready for melting ice, rising sea level, floods, droughts, weather extremes, and changing, stressed ecology. We need zoning and other policies to stop people from moving into low-lying coastal cities and areas that will be more prone to flooding and drought. We need to breed and genetically engineer crops that will handle extremes. We need to anticipate where water shortages will arise and build needed infrastructure or shift how the land is used. We need to protect and manage ecosystems with a view to how they will change and move, preserving corridors for migration and dispersion. We need to establish and maintain a global bank for the DNA and viable tissue of all known species and new species as they are described, as a safety net against extinction. Most of all, we need to fasten our political will to action now. Who knows? If we accept the realities of adaptation, maybe the picture will be so vivid, ugly, and expensive that we'll address mitigation too.
 2011 International Energy Outlook ("EIA Outlook"), page 139. Tons are metric tons.
 The EIA reference case has annual estimates for world CO2 production for 2008 through 2035 (accessed through its "Interactive Table Viewer" at http://22.214.171.124/forecasts/ieo/world.cfm). These total 1.019557 trillion tons of CO2, and that number is multiplied by 12/44 to convert it to 278.1 billion tons of carbon emissions.
 Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia, National Research Council, 2011. "[O]ur best estimate . . . is that 1,000 gigatonnes [1 trillion tons] of anthropogenic carbon . . . emissions lead to about 1.75 C increase in global average temperature." At 16. The issue is addressed in detail in section 3.4 at page 97 et seq., and the report concludes that "global mean temperature change is almost linearly related to cumulative carbon emission and is independent of the time during which the emissions occur . . ." At 98.
 The EIA reports 2008 solar energy production as 13 billion kilowatt-hours and estimates that it will be 191 billion kilowatt-hours in 2035 (EIA Outlook, Table 13, page 91). The EIA Outlook (Table 1, page 9) reports total world energy production as 504.7 quadrillion Btu in 2008 and estimates that it will be 769.8 quadrillion Btu in 2035. The EIA uses 1 kWh = 3,412 Btu (which converts to 1 trillion watt-hours = 0.003412 quadrillion Btu), hence the EIA estimate for world solar energy production expressed in Btu is 0.044356 quadrillion Btu in 2008 and 0.65169 quadrillion Btu in 2035. These numbers are used to calculate the 2008 and 2035 percentages for solar energy as a share of total energy production, and the same is done in this article for wind and hydro energy. Different units are conventionally used to report energy, including Btu, million tons of oil equivalent, joules, calories, and watts. Use of these different terms varies with kind of fuels or energy use but fortunately the different units can be converted to each other.
 The EIA reports 2008 wind energy production as 210 billion kilowatt-hours (0.71652 quadrillion Btu) and estimates that it will be 1,462 billion kilowatt-hours (4.9883 quadrillion Btu) in 2035 (EIA Outlook, Table 13, page 91).
 The EIA reports 2008 hydro energy production as 3,121 billion kilowatt-hours (10.649 quadrillion Btu) and estimates that it will be 5,620 billion kilowatt-hours (19.175 quadrillion Btu) in 2035 (EIA Outlook, Table 13, page 91).
 Using coal will estimate the high end of carbon avoidance, since oil and natural gas would also be in the mix of fossil fuels used if solar, wind, and hydro are not and are less carbon intensive. Approximately 2.095 pounds of CO2 emissions are produced per KW-Hr of energy produced with coal, which converts to 950,276 tons of CO2 emissions per trillion watt-hours or 259,166 tons of carbon emissions (EIA Report: Carbon Dioxide Emissions from the Generation of Electric Power in the United States, Table 1. July 2000).
 EIA reference case estimates of solar, wind, and hydro energy production for the years 2008 through 2035 ("Interactive Table Viewer," endnote 2) are summed in trillion watt-hours and each sum plus the total of all three sources of energy is multiplied by 259,166 tons of carbon emissions per trillion watt-hours of coal burned. Those products are multiplied by 1.75 C /1,000,000,000,000 tons of carbon emissions to estimate the temperature rise expected if coal were burned in lieu of solar, wind, and hydro energy.