Whilst there is still a vocal minority that dispute anthropogenic climate change it is now accepted by the vast majority of the scientific community. The IPCC (2013) state warming of the climate caused by human influence is unequivocal and Cook et al. (2016) have showed in more than one study that 97% of scientists agree on the causes of climate change.
Recent changes in the global climate are unprecedented over millennia and will continue long into the future as the result of the greenhouse gas emissions and land use changes that have already occurred. The main sources of greenhouse gases are fossil fuel burning, agriculture and deforestation. Concentrations have increased by about 40% since 1750 with the majority happening since the 1970s. Ice cores suggest concentrations are now higher than at any other time over at least the last 800,000 years.
There has been no measurable long-term change in solar output that could explain this rise in global temperatures.
As a result of this, Earth’s combined land and ocean surface temperature has warmed by 0.85oC between 1880 and 2012 and the number of hot days and nights has increased over most land areas. This warming has resulted in significant reductions in ice and snow cover across the world with Arctic sea ice extending 40% less than in the 1970s.
Climate change is also impacting on regional precipitation cycles with Europe and North America experiencing increases in either the frequency or intensity of heavy precipitation events. In contrast, there has been an increased frequency and intensity of drought events in the Mediterranean and parts of Africa.
Sea levels have risen by about 20cm since 1901. Interestingly the majority of this rise is not down to glacial and ice sheet meltwater but is actually due to a process of thermal expansion. Thinking back to Chemistry at school, this is the increased activity of molecules at higher temperatures resulting in an increase in volume.
By 2100, and under a high emissions scenario, global mean surface temperature could increase by another 2.6-4.8oC. With strong emission reduction this could be limited to 0.3-1.7 degrees. Precipitation and drought trends would increase in intensity and global ocean temperatures in the upper 100m will increase by 0.6-2.0oC. The Arctic could become ice free by 2050. Global mean sea-level is projected to accelerate further, with an additional rise of 0.26-0.55m. Even modest sustained warming of 2oC above pre-industrial levels is estimated to lead to sea-level rise of at least 4m over the next 2000 years.
Drawing on the largest scientific knowledge base to date, the IPCC has concluded that global warming will increase the likelihood of severe, pervasive and irreversible consequences in most world regions. The risks can be reduced both through mitigation and adaptation. These are also linked to other areas of sustainable development, in particular the protection of biodiversity and food & energy security (GMT 8).
The IPCC estimates that the 2oC scenario will result in moderate risk to the global ecosystem, but will have a very high risk for unique and threatened systems including the Arctic sea-ice ecosystem, coral reefs and the Amazon rainforest. Coral reefs will face significant pressures due to the combined effects of ocean warming, acidification and local stressors (pollution and eutrophication) (GMT 10).
For people, the ocean changes will likely result in a redistribution of marine species, with decreases in the catch potential of fisheries at tropical latitudes and associated implications for livelihoods. Throughout the 21st century, climate change is also projected to slow the rate of economic growth, increase inequality, erode food security and increase the displacement of people, particularly in low-income developing countries (GMT 1).
With continued sea-level rise, low-lying areas are very likely to increasingly experience severe impacts through coastal flooding and coastal erosion. Indeed, flood losses in 136 major coastal cities around the globe could total USD 1 trillion or more annually by 2050 unless protection is upgraded.
Another significant economic impact is the money still be spent to this day searching for more and more fossil fuel reserves when much of what is already on the asset books of companies around the world cannot be burnt to achieve the 2oC target. If this is upheld then these companies could see massive devaluations that could affect the global economy.
As a final point, in a study by Kraxner et al. (2013), they found that with rising populations and projected consumption levels there will not be enough land to simultaneously conserve all remaining natural ecosystems, halt forest loss and switch to 100% renewable energy.