Intergovernmental Panel on Climate Change (IPCC) report states: “It is unequivocal that human influence has warmed the atmosphere, ocean and land. Human emissions of carbon dioxide and other greenhouse gases are a primary driver of climate change and present one of the world’s most pressing challenges. This link between global temperatures and greenhouse gas concentrations – especially CO2 – has been true throughout Earth’s history.
Over the last few decades, global temperatures have risen sharply — to approximately 0.7℃ higher than our 1961-1990 baseline. When extended back to 1850, we see that temperatures then were a further 0.4℃ colder than they were in our baseline. Overall, this would amount to an average temperature rise of 1.1℃.
Atmospheric concentrations of CO2 did not exceed 300 parts per million (ppm) over a very long period. This changed with the Industrial Revolution and the rise of human emissions of CO2 from burning fossil fuels. We see a rapid rise in global CO2 concentrations over the past few centuries, and in recent decades in particular. For the first time in over 800,000 years, concentrations did not only rise above 300ppm but are now well over 400ppm.
Climate change has caused substantial damages, and increasingly irreversible losses, in terrestrial, freshwater and coastal and open ocean marine ecosystems.Approximately half of the species assessed globally have shifted polewards or, on land, also tohigher elevations. Some losses are already irreversible, such as the first species extinctions driven by climate change. Other impacts are approaching irreversibility such as the impacts of hydrological changes resulting from the retreat of glaciers, or the changes in some mountain and Arctic ecosystems driven by permafrost thaw.