How certain are scientists that humans are causing global climate change?

Answer 1

Temperature readings taken from around the world since 1850 prove that the global average temperature has risen by around 0.75 degrees Celsius, so there is no question that there has been a rise in average global temperatures.

Scientists proved in the nineteenth century that greenhouse gases are responsible for keeping the world some 30 degrees Celsius warmer than it otherwise would be. In 1896, Arrhenius completed a laborious numerical computation which suggested that cutting the amount of carbon dioxide (CO2) in the atmosphere by half could lower the temperature in Europe some 4-5°C (roughly 7-9°F) - that is, to an ice age level. Arrhenius made a calculation for doubling the CO2 in the atmosphere, and estimated it would raise the Earth's temperature some 5-6°C (averaged over all zones of latitude). His calculations did not take into account the effect of the oceans in ameliorating the effect of rising carbon dioxide levels, and in any case Arrhenius and other researchers were only interested in explaining the Ice Ages. No scientist at the time seriously believed that global warming was coming, but they had demonstrated that changes in carbon dioxide levels would cause global warming.

However, chemical analysis of the atmosphere has since shown that atmospheric CO2 concentrations have increased by some 35 per cent since the beginning of the Industrail Age, from the long-term average of 260-280 parts per million (PPM) to the present level of over 400 PPM. Scientists say that by burning fossil fuels, we are now releasing nearly 30 billion metric tons of carbon dioxide annually, in addition to the emissions from cement manufacture and deforestation. Analysis of the proportions of atmospheric carbon isotopes C12, C13 and C14 also proves that most of the increased levels of atmospheric CO2 do come from fossil fuels.

Most climate scientists do believe that human activities have been a significant factor in global warming and consequent climate change.

Answer 2

The vast majority of scientists agree that human activities, such as burning fossil fuels and deforestation, are the primary drivers of global climate change. This consensus is supported by a wealth of scientific evidence, including temperature records, satellite data, and computer models. Despite some uncertainties in predicting future impacts, the connection between human activities and climate change is widely accepted within the scientific community.