The Physical Science Basis

Human activities cause a major perturbation to the climate system by emissions of greenhouse gases. The Working Group I explores the current state of knowledge related to this human influence on the climate system, how it operates, how unusual it is, and what are the implications.

The Working Group I relies on studies from tens of thousands of scientists worldwide, to understand what are the current changes in climate at the global (planetary) and regional scales, how they compare with past changes, what are the causes for observed changes, how are the different components of the climate (ocean, atmosphere, land, cryosphere) interconnected and how does natural and human perturbations affect their interactions and what are the future plausible changes at the global and regional scales depending on what people chose to do.

The scientific topics covered by Working Group 1 include:

• The effect of atmospheric composition on climate (greenhouse gases, small particles, etc.)
• Temperature changes in the atmosphere, over land and in the ocean
• Rain and snow changes; drought
• Extreme weather events intensity and frequency
• The attribution of observed changes to natural variability or human activity
• Glaciers and ice sheets melting; permafrost thawing
• Ocean and sea level rise
• How carbon moves through the air, the atmosphere, plants and the ocean
• Which fraction of our carbon emissions can be stored in the ocean, the vegetation and soils
• Interactions between climate and land
• Links between climate and air quality
• The possible future climates depending on climate action or inaction
• The amount of carbon emissions compatible with climate goals
• The Working Group I report provides a clear picture of how human-induced changes are emerging from the natural climate variability at the global and regional scales.

The Sixth Assessment Report

The first part of the report assesses the global scale phenomena – observations, how these are attributed to human influence, and then explores different future scenarios of how the climate will change in the future depending on future human choices.

The second part of the report is dedicated to the components of the climate system (ocean, atmosphere, land, cryosphere) and their interactions through the carbon or the water cycles and how the climate system responds to changes in the composition of the atmosphere.

The final part of the report assesses how global scale change affects extremes such as drought, storms and flooding, as well as other factors that may cause impacts to natural, managed and human systems. The report also includes an Interactive Atlas which allows users to select a region, a dataset, and explore climate information, including simulations of future climate change.