IPCC 2021: How have humans impacted the climate?

The world’s top scientists have warned that there is unprecedented warming of the planet because of human influence. The Intergovernmental Panel on Climate Change (IPCC), the apex climate change scientific body, has just released the sixth assessment report (AR6) on climate change.

The land and oceans have absorbed 56 per cent of carbon dioxide (CO2) emissions from human activities over the past six decades, the report said. Temperatures have increased by an average of one degree Celsius due to human-activity from 1850–1900 to 2010–2019.

Human activity is also the main cause of the global retreat of glaciers since the 1990s and the decrease in Arctic sea ice area.

In 2019, atmospheric CO2 concentrations were the highest in two million years, methane and nitrous oxide were highest in 800,000 years. Temperatures in 2011–2020 are more than the most recent warm period, around 6,500 years ago (0.2°C to 1°C relative to 1850– 1900).

The oceans have warmed faster in the 20th century than the last deglacial transition around 11,000 years ago. Extreme heat waves have become more frequent and more intense across most land regions since the 1950s. Cold extremes including cold waves have become less frequent and less severe.

Human activity has also increased agricultural and ecological droughts in some regions due to increased land evaporation.The proportion of major tropical cyclones has increased over the last four decades. The probability of simultaneous heatwaves and droughts and flooding in some locations have also increased. Increase in temperatures has caused global sea-level rise through ice loss on land and thermal expansion from ocean warming.