What should the CO2 limits for Global Warming be?

Answer 1

We don't know exactly what levels of carbon dioxide (CO2) will limit global warming to a rise of 2 degrees Celsius, which is the maximum temperature rise recommended to avoid dangerous effects of climate change. The problem is that CO2 stays in the atmosphere for many hundreds of years. Levels now (2016) are over the 400 ppm (parts per million) or 0.04%, and this CO2 will keep absorbing heat. Even after 1000 years some of this carbon dioxide will still be in the atmosphere.

Scientists tell us that we must reach peak greenhouse gas emissions by 2020. That means that after 2020 our emissions should be reducing every year.

The United Nations Environment Program (UNEP)'s Emissions Gap Report in 2015 reports that global emissions in 2010 were 47.5 GtCO2e, and suggests that emission levels of 52 GtCO2e in 2020, 42 GtCO2e by 2030 and by 2050 close to 22,are consistent with a “likely” chance of limiting global warming to 2° C.

(GtCO2e means gigatons of CO2 equivalent, in other words, all greenhouse gases.)

Read The Gap Report here.

Answer 2

The CO2 limits to prevent global warming from exceeding 1.5-2 degrees Celsius are generally seen as around 350-450 parts per million (ppm) in the atmosphere. This is in line with the goals outlined in the Paris Agreement to keep global temperature rise well below 2 degrees Celsius above pre-industrial levels.