The World Meteorological Organisation (WMO) has published its annual Greenhouse Gas Bulletin which reports that in 2016, the global concentration of CO2 had attained its greatest level in 800,000 years (Figure), reaching 403.3 ± 0.1 parts per million (ppm), from 400.0 ± 0.1 ppm in the previous year, which is 145% of pre-industrial levels (i.e. prior to the year 1750,when it stood at 278 ppm). The Bulletin cites data from the US National Oceanic and Atmospheric Administration, which show that there has been an increase in the combined radiative forcing (global heating effect) from all long-lived greenhouse gases by 40% since 1990, which rose by 2.5% in the space of just one year (2015-2016). The report states that [such] “rapidly increasing atmospheric levels of CO2 and other greenhouse gases (GHGs) have the potential to initiate unpredictable changes in the climate system, because of strong positive feedbacks, leading to severe ecological and economic disruptions.” The numbers quoted in the WMO Bulletin are provided by the WMO Global Atmosphere Watch Programme, whose function is to monitor levels of greenhouse gases and provide an “early warning system” for significant changes in these atmospheric gases which are critical agents of climate change.
Ice-core measurements show that the rate at which the atmospheric level of CO2 has grown over the past 70 years is 100 times greater than that which prevailed at the end of the previous ice age. The WMO further notes that, “the steady increase in GHG concentrations in the atmosphere over the observation period from 1970 until present is consistent with the observed increase of global average temperatures in the same period with a record measured in 2016, as reported in the WMO statement on the state of the global climate.”
Combined with a strong El Niño event in 2015 and 2016, emissions from human activities (mainly burning fossil fuels, and changes in land use) have given rise to the observed record increase in atmospheric CO2 concentration, which will urge a yet greater increase in climate forcing. The Secretary-General of the WMO, Petteri Taalas, is quoted as saying:
“CO2 remains in the atmosphere for hundreds of years and in the oceans for even longer. The laws of physics mean that we face a much hotter, more extreme climate in the future. There is currently no magic wand to remove this CO2 from the atmosphere.”
Such high atmospheric CO2 concentrations have not existed since 3-5 million years ago, when the mean global temperature was 2-3 oC warmer than it is presently, with sea levels 20-30 metres greater than now, due to the melting of the Greenland and West Antarctic ice sheets, and part of the East Antarctic ice. Atmospheric greenhouse gas concentrations are a result of the complex interplay between various components of the Earth system, namely the atmosphere, biosphere, cryosphere and the oceans. About a quarter of all greenhouse gases are absorbed by the biosphere and another quarter by the oceans, which therefore act as a buffer to the amounts of them that remain in the atmosphere. Of the other greenhouse gases, both nitrous oxide (N2O) and methane (CH4), reached new record concentrations of 328.9 ± 0.1 ppb and 1,853 ± 2 ppb respectively. Thus, the concentrations of CO2, and N2O have increased to 145% and 122% of pre-industrial levels, with methane showing the most substantial increase, to 257% of its level before 1750. As Mr Taalas has summarised the situation:
“Without rapid cuts in CO2 and other greenhouse gas emissions, we will be heading for dangerous temperature increases by the end of this century, well above the target set by the Paris climate change agreement. Future generations will inherit a much more inhospitable planet.”
This view is reinforced by provisional figures from the WMO which indicate that 2017 is “very likely” one of the 3 warmest years on record, and is likely to be the hottest year in the absence of an El Niño event. The WMO has stated that the average global temperature during January-September 2017 was 1.1 oC higher than in pre-industrial times, and is perilously close to the 1.5 oC threshold believed to be essential to the survival of many island states that are vulnerable to rising sea-levels. The indication is that 2017 is likely to prove 0.47 oC warmer than the average during the period 1981-2010. While it will be necessary for WMO scientists to perform attribution studies to make definite links between the extreme weather events in 2017 and rising temperatures, they believe that the influence of climate change can be seen in such phenomena as temperatures exceeding 50 oC in Asia and the train of hurricanes witnessed in the Caribbean and the Atlantic, earlier in the year. Warmer waters can provide larger amounts of energy to storms, while rising sea levels make the consequent flooding more devastating. 2017 was the first year on record during which two category 4 storms hit the U.S. mainland, while Hurricane Irma was the longest running Category 5 storm on record, where rain gauges in Texas recorded 1,539 mm - another record for a single weather event on the U.S. mainland. In contrast, Africa and South America were severely impacted by droughts and heatwaves. As a consequence, more than 11 million people are currently experiencing extreme food insecurity in Ethiopia, Kenya and Somalia.