Climate change: evidence and causes

Answers to key questions

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

Project background

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 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.

The Support for the 2014 Edition was provided by NAS Endowment Funds. We offer sincere thanks to the Ralph J. and Carol M. Cicerone Endowment for NAS Missions for supporting the production of this 2020 Edition.

Find out more about the Royal Society's work on climate change on our Basics of Climate Change page, or explore our interactive net-zero carbon infographic.

Videos

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

Professor Eric Wolff - 'Past climate - future climate'

Continuing the Conversation on Climate Change