The most recent report from Working Group 3 of Intergovernmental Panel on Climate Change accepted 177 analyses from economists on mitigating climate change. 6 attempted to keep temperature increase below 2.4°C, none tried to keep temperature increase below 2°C. The goal I’ve heard most often from the climate community is for the latter, with some including James Hansen arguing for even lower increases.
Key Impacts from IPCC. By the time temperature increase reaches 2°C, hundreds of millions are expected to experience increased water stress, most/all coral will bleach, cereal productivity will increas in high latitude and decrease in low latitude (and decrease everywhere by 3.5°C or higher), millions more could experience coastal flooding each year (if ice sheet melt becomes important at this level, this number will be higher), and health burden will increase.
Burning Embers from Stern Review Click here to enlarge. Changes at 2°C may include onset of irreversible melting of Greenland ice sheet, large fraction of ecosystems unable to maintain current form, risk of weakening of natural carbon absorption and possible increasing natural methane releases.
A report from International Energy Agency too recent to be included in the IPCC report, Energy Technology Perspectives, 2008, looks at what is needed for the 2.4°C goal.
First, the warning: the best estimate of the carbon dioxide and greenhouse gas levels by 2050 could eventually raise world temperatures by 6°C or more.
From ETP 2008, Executive Summary, bullets added:
• A global revolution is needed in ways that energy is supplied and used. Far greater energy efficiency is a core requirement. Renewables, nuclear power, and CO2 capture and storage (CCS) must be deployed on a massive scale, and carbon-free transport developed.
• A dramatic shift is needed in government policies, notably creating a higher level of long-term policy certainty over future demand for low carbon technologies, upon which industry’s decision makers can rely.
• Unprecedented levels of co-operation among all major economies will also be crucial, bearing in mind that less than one-third of “business-as-usual” global emissions in 2050 are expected to stem from OECD countries.
• [T]he global energy economy will need to be transformed over the coming decades.
The IEA report focuses on carbon dioxide from energy, ignoring other greenhouse gases. Currently, the world produce 28 gigatonnes (billion metric tons) of CO2 each year. Since business as usual is expected to get us to 62 GtCO2, cutting by 50% to 14 Gt will require us to cut back 48 Gt.
More details later.