All illustrations from the IPCC 6th Assessment Report, Vol. 3, Chap. 2. Modeled CO2 and other GHG emissions to 2100 under various scenarios. (CurPol = current policies; ModAct = moderate action; [LD,Ren,SP] = phase-out of fossil fuels; Neg = carbon capture employed, fossil fuels still used)
Contributions of CO2 and other gases in CO2 equivalents (including sinks) to 2100. (C1: below 1.5C, no or limited overshoot; C2: belowe 1.5C, high overshoot; C3: likely below 2C; C4: below 2C; C5: below 2.5C; C6: below 3C; C7: below 4C; C8: above 4C)
Limiting global warming to 2.0C/3.6F by 2100 will require, according to models, lowering emissions from GtCO2eq-yr-1 30-49 in 2030 to 13-27 GtCO2eq-yr-1 in 2050. This goal would require eliminating the burning of coal and dramatically reducing the burning of oil and gas. It also requires reducing acreage cleared for farming, and reforesting about 322 million ha/796 million acres globally.
Socioeconomic trends to 2100. (SSP1: Sustainability (Taking the Green Road); SSP2: Middle of the Road; SSP3: Regional Rivalry (A Rocky Road); SSP4: Inequality (A Road divided); SSP5: Fossil-fueled Development (Taking the Highway) )
Total emission profiles to 2100 under different scenarios.
Though any reforestation is helpful in mitigating climate change, forests are not equivalent, due to their other related effects on the biosphere. Specifically, ongoing loss of the Brazilian rainforest will threaten the entire monsoonal climate of northern South America, because it is the forest itself which drives the seasonal circulation of winds. Removal of enough rainforest will end that entire aspect of world climate for the foreseeable future.
Emissions by source with different scenarios.
Reducing energy use—limitation of the demand side, in economic terms—is also essential to limiting global warming to 2°C. In the 77 (as of this writing) years remaining between now and 2100, these changes in energy production and consumption must be front-loaded—occurring mostly between now and 2050—to prevent overshoot past 2°C.
Global temperature rise by scenario.
The hard pill to swallow, which makes these scenarios all the more difficult to accomplish, is the expected loss in global GDP. It cannot be avoided or denied that reducing and eliminating the most convenient, and still very abundant, energy sources we have will harm economic growth, especially if energy transitions occur quickly and soon. Perhaps the single biggest obstacle to meaningful global action on climate change and environmental sustainability in general is defeating the concept of limitless economic growth, which is impossible on a planet with finite physical resources. IPCC models show that limiting global warming to 2°C will result in a decline of global GDP of 1.3-2.7% by 2050; limiting it to 1.5°C will result in a decline of 2.6-4.2%.
Correlation of emissions to global temperature rise.
These losses must be looked at in opposition to the cost of doing nothing which, if climate impacts are in the moderate to high range of projection, will have an even greater drag on GDP and incur far greater costs than up-front mitigation. As with the physical effects of global warming, the costs of mitigation vary regionally across the globe, with the physically more vulnerable areas (low-lying coasts, and hot and arid zones especially) needing more investment. In short, it is still possible, though less so with passing time, to change our energy use around the world enough to avoid the most extreme warming scenarios, and avoid the catastrophic economic toll they would bring.
Tomorrow: near- and mid-term mitigation strategies.
Be brave, be steadfast, and be well.
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