8. Is there a point at which adding more CO2 will not cause further warming?

No. Adding more CO2 to the atmosphere will cause surface temperatures to continue to increase. As the atmospheric concentrations of CO2 increase, the addition of extra CO2 becomes progressively less effective at trapping Earth’s energy, but surface temperature will still rise.

Our understanding of the physics by which CO2 affects Earth’s energy balance is confirmed by laboratory measurements, as well as by detailed satellite and surface observations of the emission and absorption of infrared energy by the atmosphere. Greenhouse gases absorb some of the infrared energy that Earth emits in so-called bands of stronger absorption that occur at certain wavelengths. Different gases absorb energy at different wavelengths. CO2 has its strongest heat-trapping band centred at a wavelength of 15 micrometres (millionths of a metre), with wings that spread out a few micrometres on either side. There are also many weaker absorption bands. As CO2 concentrations increase, the absorption at the centre of the strong band is already so intense that it plays little role in causing additional warming. However, more energy is absorbed in the weaker bands and in the wings of the strong band, causing the surface and lower atmosphere to warm further.

Questions and answers

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1. Is the climate warming?
2. How do scientists know that recent climate change is largely caused by human activities?
3. CO2 is already in the atmosphere naturally, so why are emissions from human activity significant?
4. What role has the Sun played in climate change in recent decades?
5. What do changes in the vertical structure of atmospheric temperature – from the surface up to the stratosphere - tell us about the causes of recent climate change?
6. Climate is always changing. Why is climate change of concern now?
7. Is the current level of atmospheric CO2 concentration unprecedented in Earth’s history?
8. Is there a point at which adding more CO2 will not cause further warming?
9. Does the rate of warming vary from one decade to another?
10. Does the recent slowdown of warming mean that climate change is no longer happening?
11. If the world is warming, why are some winters and summers still very cold?
12. Why is Arctic sea ice reducing while Antarctic sea ice is not?
13. How does climate change affect the strength and frequency of floods, droughts, hurricanes and tornadoes?
14. How fast is sea level rising?
15. What is ocean acidification and why does it matter?
16. How confident are scientists that Earth will warm further over the coming century?
17. Are climate changes of a few degrees a cause for concern?
18. What are scientists doing to address key uncertainties in our understanding of the climate system?
19. Are disaster scenarios about tipping points like ‘turning off the Gulf Stream’ and release of methane from the Arctic a cause for concern?
20. If emissions of greenhouse gases were stopped, would the climate return to the conditions of 200 years ago?

Your questions

In addition to the 20 key questions answered in 'Climate Change: Evidence & Causes', we asked for your questions about the science of climate change on Google Moderator.

View all questions and our responses.

Download the answers (PDF).