Working Group I summary report

The Physical Science Basis of Climate Change, assessed current scientific knowledge of the natural and human drivers of climate change, observed changes in climate, the ability of science to attribute changes to different causes, and projections for future climate change.

The report provides persuasive evidence of climate change and included advanced observations of the climate system. It presented new projections of future global climate change using results from 19 climate models, with improved representations of physics, chemistry, and spatial resolution.

The key areas:

• Observing climate change — warming has now been observed across the Earth system. The atmosphere, land observations and even data from below the surface of the oceans have all shown this warming trend. In the past, there have been some apparent inconsistencies between measurements from different parts of the system. Now, in this report, there is far greater certainty that the planet is undergoing warming.
• Causes of planetary warming — this report provided new evidence that humans have played a major part in the observed warming trend. Human activity, through the generation and release of greenhouse gases, has been a significant contributory factor in the global temperature rise.
• The future — as the climate changes, the challenges are likely to be profound. Understanding what aspects of the weather and climate will change most rapidly is important. With research showing that the climate is changing faster with increased incidence of extreme weather, what will the climate look like in the years to come? What will our day-to-day weather be like? Government and other decision-makers need the best advice possible, so they can make informed decisions. The issue is a big one and it is important that the science addresses the uncertainty and helps provide answers.