Scientists have developed an understanding of the Earth’s climate system through years of observations, theory development and model building. We know with high confidence that climate change is happening today and is the result of greenhouse gas emissions caused by human activity. Impacts from climate change are already being felt today and will continue to increase in the future. Action to limit future global greenhouse gas emissions will help restrict future changes in the climate system.
There is no clear threshold where climate change moves from safe to dangerous. We can expect some disruptions and irreversible losses of natural habitats and resources, even with a 1.5 or 2°C temperature rise. However, with rapid global action to cut greenhouse gas emissions, we can still reduce the likelihood of global temperatures increasing by more than 1.5 – 2°C. On the other hand, if we take no action, global temperatures could increase by 4°C or more by the end of the century.
The rising global temperature will be increasingly prevalent and will lead to wider changes to our weather. Additionally, many impacts of climate change are already being detected, including:
- warming of the troposphere (the lower part of the atmosphere)
- acidification of the oceans
- rising sea levels
- declining glaciers and sea ice
- slowing of increases to crop productivity
What is causing climate change?
Geological records stretching back millions of years indicate a number of large variations in Earth’s past climate. However, comprehensive assessment by scientists shows that it is extremely likely that human activity has been the dominant cause of warming since the mid-20th Century.
Measuring a warming world
Measuring the climate system from the ground, in the oceans and from space provides numerous signs of the Earth’s changing climate.