The planet’s leading international network of climate change scientists have issued a new and damning report of the impact of human activity on global warming. The study concluded that global warming is unequivocally real and that human activity is the main driver causing most of the rise in temperatures since 1950. The report said global warming is contributing to rising sea levels and unpredictable weather. The report is another cold, factual document which demands the worlds' governments take urgent action to address the problem.
Yesterday, the Intergovernmental Panel on Climate Change (IPCC) released their summary report about the human impact on climate change from their meeting in Paris. The report stated that global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased greatly as a result of human activity since the start of the Industrial Age in 1750. Based on measurements from ice cores spanning many thousands of years, these concentrations now far exceed pre-industrial values.
Carbon dioxide is the predominant greenhouse gas and global concentrations have increased from 280 parts per million (ppm – the ratio of greenhouse gas molecules to the total number of molecules of dry air) in 1750 to 379 ppm in 2005. The report says the primary cause of this increase is the use of fossil fuels with land use also a contributing factor. Though there is year on year variability, annual carbon dioxide emissions are now increasing at a rate of 1.9 ppm in the last ten years compared to a growth rate of 1.45 ppm in the 45 years since measurements started in 1960.
The growth rate in methane concentration is also startling. Its pre-industrial average was 715 parts per billion (ppb) and was recorded as 1774 ppb in 2005. This latter figure is far greater than the natural range of methane measured in ice cores over the last 650,000 years which was 320 to 790 ppb. The scientists rated it a greater than 90% chance that this increase was the result of human agriculture and fossil fuel use. Meanwhile nitrous oxide has increased from 270 ppb in 1750 to 319 ppb in 2005, with a constant growth rate since in 1980.
The report also noted that eleven of the past 12 years (1995-2006) rank among the 12 warmest years since records began in 1850. The warming trend over the past 50 years is twice that of the past 100 years. Meanwhile ocean temperatures have also increased and the oceans have absorbed 80% of the heat added to the climate system. This causes seawater to expand and sea levels to rise. This rise is exacerbated by retreating mountain glaciers and decreasing snow cover. New data suggests that ice sheet loss in Greenland and Antarctica have contributed to the sea level rise between 1993 and 2003. During this decade sea levels rose about 3.1 mm a year though it is not clear if this is an anomaly or an increase in the longer-term trend.
The report states that climate change has been observed in many indicators such as the Arctic ice flow, rainfall, ocean salinity, wind patterns, and the incidence of extreme weather such as droughts, deluges, heatwaves and cyclones. Arctic temperatures increased at twice the global average in the last century while sea ice shrank by 2.7% per decade. Rainfall has increased dramatically in the eastern part of both Americas, northern Europe and central Asia but has decreased in the African Sahel, the Mediterranean and the south of Africa and Asia. These patterns are affected by the increasing salinity of low latitude waters and the lower salinity of mid and high latitude waters.
The report included a paleoclimatic perspective which has historical and applied scientific objectives. These supported the contention that the warming is unusual in the last 1,300 years. The last time polar regions were significantly warmer than the present was 125,000 years ago when the lack of polar ice caused a 4 to 6 metre rise in sea levels.
The report concluded while it was unlikely that climate change of the 7 centuries prior to 1950 were caused by human actions, it was extremely unlikely that the atmospheric and ocean warming and ice loss of the last 55 years were caused by natural forces. The report predicted a rise of 0.2 degrees Celsius per decade for the next 20 years. Continued gas emissions at or above present levels would increase it further and cause warming larger than any observed in the 20th century.
The report predicts snow cover will contract, polar sea ice will shrink and extreme weather such as heatwaves, heavy rain and tropical cyclones will become more frequent. If the entire Greenland ice sheet is lost (which could occur after 2100) it would contribute to sea level rises of about 7 metres. The scientists predict Antarctica will remain too cold for widespread surface melting.
If carbon dioxide concentrations in the atmosphere reach twice their pre-industrial levels, the global climate will probably warm by 3.5 to 8 degrees. But there would be more than a 1-in-10 chance of much greater warming; a situation many earth scientists say poses an unacceptable risk. With these almost irrefutable scientific conclusions, the report is a call to action for the world’s governments. The recent Stern Report detailed how the cost of reducing emissions to reduce the extent of these climate changes may well be much less than the cost of not reducing emissions and having these impacts.