Current atmospheric concentrations of carbon dioxide are higher than at any time in the last two million years. This is unequivocally caused by human activities and has produced rapid and widespread warming of the atmosphere, oceans and land on an unprecedented scale.
The effects of climate change are seen in every region of the globe in the form of extreme weather such as heatwaves, heavy precipitation, droughts and tropical cyclones, as well as dwindling glaciers and polar ice. Our climate is not merely changing, the rate of change is accelerating.
Global warming will continue to increase, exceeding 2 degrees by mid-century. A warmer climate will increase the intensity and frequency of wet and dry weather and amplify rainfall variability related to the El Nin~o–Southern Oscillation.
The oceans have warmed to depths below 2000 metres and are warming faster than at any time since the end of the last ice age. The Indian Ocean and western equatorial Pacific Ocean have warmed faster than the global average, with more frequent marine heatwaves projected for the western tropical Pacific and the Arctic Ocean.
Since 1901, the global mean sea level (GMSL) has risen by about 20cm and the rate of rise is accelerating. GMSL is predicted to rise by up to a metre by 2100 and increases of between 2–5m by 2150 “cannot be ruled out.” This would be catastrophic for Pacific island nations which could become entirely submerged.
Rising sea levels around Australia have already impacted heavily populated coastal areas and, if CO2 emissions remain high, sandy shorelines could retreat by more than 200 metres in many locations by the end of the century.
Warming, acidification, deoxygenation and marine heatwaves will continue to increase throughout this century, posing major challenges for fragile marine environments like the Great Barrier Reef. The geographic range and seasonal life cycles of many marine organisms have already shifted towards the poles and to greater depths in search of cooler waters, altering species composition and disrupting ecosystems.
The science is irrefutable, and the message is clear — only immediate and sustained reductions in CO2 emissions and greenhouse gases can avert a global climate disaster.
For the full IPCC report visit: ipcc.ch/report/ar6/wg1.