Climate Change 2021: Summary for All – published Version 2 – 15 November 2022 – Weather, Climate and the IPCC – “No matter where we live, we all experience weather: how the conditions of our atmosphere change over minutes, hours, days, weeks. We also all experience climate: the weather of a place averaged over several decades. Climate change is when these averaged conditions start to change and its causes can be either natural or caused by human activities. Rising temperatures, variations in rainfall, increased extreme weather events are all examples of climate changes, but there are many others. Back in 1990, the first report by the Intergovernmental Panel on Climate Change (IPCC) concluded that human-caused climate change would soon become apparent but could not yet confirm that it was already happening. Now, some 30 years later, the evidence is overwhelming that human activities have changed the climate. Hundreds of scientists from all over the world come together to produce IPCC reports. They base their conclusions on several kinds of scientific evidence, including:
• Measurements or observations, sometimes spanning more than a century back in time;
• Paleo (very old) climate evidence from thousands or millions of years ago (for example: tree rings, rock or ice cores);
• Computer models that look at past, current and future changes
• Understanding of how the climate works (physical, chemical and biological processes).

Since the IPCC first started, we now have much more data and better climate models. We understand more now about how the atmosphere interacts with the ocean, ice, snow, ecosystems
and land of the Earth. Computer climate simulations have considerably improved and now provide past change and future projections that are much more detailed. Plus, we have now had decades more greenhouse gas emissions, making the effects of climate change more apparent. As a result, the latest IPCC report is able to confirm and strengthen the conclusions from previous reports. What’s covered in this summary?
• Climate Change Today: what changes have already occurred and how we know humans are responsible;
• Our Future Climate: what changes could happen in the future depending on the actions we take;
• Limiting Future Climate Change: what is required to stop global temperature from continuing to rise..”