Climate Change: Evidence & Causes

27 February 2014

Sir Paul Nurse on 'Climate Change: Evidence & Causes'

Climate change is one of the defining issues of our time. It is now more certain than ever, based on many lines of evidence, that humans are changing Earth’s climate. The atmosphere and oceans have warmed, accompanied by sea-level rise, a strong decline in Arctic sea ice, and other climate-related changes.

Greenhouse gases such as carbon dioxide (CO2) absorb heat (infrared radiation) emitted from Earth’s surface. Increases in the atmospheric concentrations of these gases cause Earth to warm by trapping more of this heat. Human activities - especially the burning of fossil fuels since the start of the Industrial Revolution - have increased atmospheric CO2 concentrations by about 40%, with more than half the increase occurring since 1970. Since 1900, the global average surface temperature has increased by about 0.8 °C (1.4 °F). This has been accompanied by warming of the ocean, a rise in sea level, a strong decline in Arctic sea ice, and many other associated climate effects. Much of this warming has occurred in the last four decades. Detailed analyses have shown that the warming during this period is mainly a result of the increased concentrations of CO2 and other greenhouse gases. Continued emissions of these gases will cause further climate change, including substantial increases in global average surface temperature and important changes in regional climate. The magnitude and timing of these changes will depend on many factors, and slowdowns and accelerations in warming lasting a decade or more will continue to occur. However, long-term climate change over many decades will depend mainly on the total amount of CO2 and other greenhouse gases emitted as a result of human activities.

Project background

'Past climate -- future climate' Professor Eric Wolff

The Royal Society and the US National Academy of Sciences, with their similar missions to promote the use of science to benefit society and to inform critical policy debates, offer this new publication as a key reference document for decision makers, policy makers, educators, and other individuals seeking authoritative answers about the current state of climate change science. The publication makes clear what is well established, where consensus is growing, and where there is still uncertainty. It is written and reviewed by a UK-US team of leading climate scientists. It echoes and builds upon the long history of climate-related work from both national science academies, as well as the newest climate change assessment from the United Nations’ Intergovernmental Panel on Climate Change.

This work was kindly supported by the Raymond and Beverly Sackler US-UK Scientific Forum.

Continuing the Conversation on Climate Change

Thursday 27 February 2014
3:00pm - 4:30pm GMT

Hosted by Miles O’Brien, science correspondent, PBS Newshour
Introductions by Dr. Ralph J. Cicerone and Sir Paul Nurse

Dr. Ralph J. Cicerone, President of the National Academy of Sciences and Sir Paul Nurse, President of the Royal Society gave brief introductions. Host Miles O’Brien guided the discussion with lead authors, Professor Eric Wolff FRS of the University of Cambridge, and Professor Inez Fung of the University of California, Berkeley.

Climate Change: Evidence & Causes

Questions and answers

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).