Climate

Warming of the climate system is undeniable, and human involvement is the most dominant cause. The total natural contributions from solar irradiance changes and stratospheric volcanic aerosols have only made a small difference. Data from the International Panel of Climate Change (IPCC) is staggering. Since the 1950s, many of the observed changes are unprecedented over decades to millennia. In the Northern Hemisphere, 1983-2012 was likely the warmest 30-year period of the last 1400 years. Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent. Mean Arctic sea ice extent decreased over the period 1979 to 2012 with a rate that was very likely in the range 3.5 to 4.1% per decade (range of 0.45 to 0.51 million km2 per decade), and very likely in the range 9.4 to 13.6% per decade (range of 0.73 to 1.07 million km2 per decade) for the summer sea ice minimum.

According to the IPCC there is a high confidence that the rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two. Over the period 1901 to 2010, global mean sea level rose by 0.19m [0.17 to 0.21] There is high confidence that sustained warming greater than some threshold would lead to the near-complete loss of the Greenland ice sheet over a millennium or more, causing a global mean sea level rise of up to 7 m. Current estimates indicate that the threshold is greater than about 1°C (low confidence) but less than about 4°C (medium confidence) global mean warming with respect to pre-industrial levels.

The atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years. Carbon dioxide concentrations have increased by 40% since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions. Annual CO2 emissions from fossil fuel combustion and cement production between 2002 and 2011 were 54% higher than the 1990 level. Methane has increased by 150% and nitrous oxide by 20%. The ocean has absorbed about 30% of the by humanity emitted carbon dioxide, causing the before mentioned ocean acidification. It is also likely that human influences have affected the global water cycle since 1960 and that the global ocean will continue to warm during the 21st century. Heat will penetrate from the surface to the deep ocean and affect ocean circulation. There is also a positive feedback between climate and the carbon cycle on century to millennial time scales, meaning that an increase in temperature will by itself increase CO2 in the atmosphere.

The IPCC concludes that continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions. And even though actions are taken, most aspects of climate change will persist for many centuries even if emissions of CO2 are stopped.[1]

Inhabited Islands are being drowned by the ocean, and if action is not taken now, coastal cities will suffer the same fate.

We have entered the Anthropocene. According to Professor Johan Rockström the planet has so far been kind to us and limited our fossil fuel impact by providing negative feedback. Now however, if we don't act, we might enter a self-enforcing temperature feedback loop out of our control. We can limit the temperature increase to 2 degrees and avoid chaos. We need to have net zero fossil fuel emissions by 2050.[2] I'm sure that we can accomplish this faster. 

[1] https://www.climatechange2013.org/images/report/WG1AR5_SPM_FINAL.pdf

[2] Rockström, Johan, Lecture at Aula Magna, Stockholm University, Sweden, 2016.10.06