Under the Business-as-usual scenario (RCP 8.5) the future climates in 2030 will most closely resemble Mid-Pliocene climates, with surface temperatures 1.8 °C to 3.6 °C warmer than preindustrial temperatures. This means a climate that resembles the climate 3-3.3 million years ago, when CO2 -levels were at 400ppm – levels which we have crossed in 2016. Mid-Pliocene conditions will first emerge in continental interiors and in the decades afterward they will spread towards the coasts.
In 2100 the situation will be totally different. Under the RCP8.5 scenario, the climate from the past that best matches continental interiors by 2100 is the early Eocene climate. For these climate conditions, we have to go back abut 50 million years, when global mean annual surface temperatures were a whopping 13 °C ± 2.6 °C higher than preindustrial temperatures and there were swampy forests in the arctic.
Under the RCP4.5 emission scenario the climate stabilizes at mid Pliocene-like conditions.
Researchers at the University of South Wales, using data from 43,000 rainfall stations and 5,300 river monitoring sites across 160 countries, have found (2018) that water supplies worldwide are decreasing. Despite growing precipitation due to climate change, higher evaporation rates and dryer grounds that soak up more water leads to less water in rivers.
This study is in line with a study from 2009, that points out that world’s major rivers, amongst which the Yellow river in Northern China and the Ganges in India, are ‘drying up’. Causes are human activities such as dam building and diverting water for agriculture (that caused e.g. the Aral Sea to disappear) and climate change altering rainfall patterns and increasing evaporation rates. The only exceptions are rivers in the Arctic, the Brahmaputra in South Asia and the Yangtze in China. Very much likely because of additional melting of glaciers and ice sheets.
Experts predict that water levels of Euphrate and Tigris might drop 30-70% compared to end 20th century and speak about the “Fertile Crescent” disappearing altogether. Even notoriously wet places such as the United Kingdom are expecting severe water shortages by 2050s as summers get drier. The Colorado river has no longer enough water to go around.
Most of northern china suffers from acute water shortage (multicausal). In the past 25 years, 28,000 rivers and waterways have disappeared across the country. The iconic Yellow River, the second-longest in Asia, is now a tenth of what it was in the 1940s, and often fails to reach the sea. Former Chinese premier Wen Jiabao has warned the lack of water threatened the very survival of the Chinese nation itself.
A United Nations report of 2009 estimated the number of people to be displaced internally in 2045 by desertification alone around 135 million.
The UN International Organization for Migration forecasts 200 million internal and international (permanent and temporary) environmental migrants by 2050.
A paper from June 2017 (by Geisler et al) mentions 1.4 billion people that could be climate refugees by 2060 due to rising ocean levels (alone!). A number that societies might not be able to support: “The colliding forces of human fertility, submerging coastal zones, residential retreat, and impediments to inland resettlement is a huge problem. We offer preliminary estimates of the lands unlikely to support new waves of climate refugees due to the residues of war, exhausted natural resources, declining net primary productivity, desertification [and] urban sprawl…”
12 million hectares of productive land become barren every year due to desertification and drought (alone), while food production needs to increase by 70% in 2050 to feed the entire world population. Drought, water scarcity and destruction of natural resources because of climate change (and overpopulation, etc.) might lead to conflict. The UNCCD reminds that 40 per cent of all intrastate conflicts in the past 60 years are linked to the control and allocation of natural resources.
In addition to a weakening gulf stream,another factor that contributes to colder winters (and probably warmer summers) in the northeastern United States, Europe, and especially Asia, is a weakening jet stream. The jet stream is a wind of about 180 km/h on average and up to 400 km/h in instances, that streaks around the north pole at 8km altitude. It gets its power from temperature differences between south and north. It is weakening because the arctic is warming fast. Warming in the arctic means less sea ice, which means more – dark – ocean that in turn absorbs more heat (i.e. a positive feedback loop).
A weaker jet stream meanders more, bringing warmer air to pockets in the arctic and colder air to pockets south. These ‘loops’ in the jet stream can get stuck, bringing about extreme events of cold spells and probably also heat and drought. Based on changes in the jet stream researcher predicted worsening drought in California back in 2004. The weaker jet stream does not mean that cold spells get colder though, cold extremes are getting less cold.
3-3.3 million years ago global average temperature was 2-3 °C higher than today. The sea level was 25 meters higher and there was hardly any ice sheet in the northern hemisphere. Just as in predictive models, in the paleaontological data you also see a larger difference with today’s temperatures in the northern hemisphere than in tropical regions and southern hemisphere.
Carbon dioxide concentration during the mid-Pliocene has been estimated at around 400 ppm (yes, the 400 ppm that we have crossed in 2016 for the first time in 3 million years).
The climate was not only warmer, but also wetter, resulting in a northward shift of the taiga (boreal forest) and tundra and a spread of tropical savannahs and woodland in Africa at the expense of deserts (am I reading this correctly: less desert?!)
The Guardian dedicates an article to where you can best live in the U.S. when climate change gets serious. Broadly speaking you can best move to a band roughly above the 42nd parallel.
Places close to a reliable source of water without being flood-prone score high. Seattle, Buffalo, New York (with flood defenses), and Duluth, Minnesota are mentioned as places you might want to be at the end of the 21st century. Places that score low are the south-west and south-east because they will be baked. Southern Florida will be submerged and the Gulf coast will be battered by hurricanes.
Researchers show in Science Advances that the probability of extremely warm and extremely dry conditions has doubled worldwide.
They warn for the threat this poses to worldwide agricultural production. Before anthropogenic climate change chances of extreme weather in multiple agricultural key regions were slim. At the same time the global marketplace could compensate for a bad harvest in one region. The researchers see erosion of this buffer. They specifically point out that the frequency of these simultaneous extreme hot and dry conditions will increase with 20% in the next three decades.
If climate change is unchecked (RCP 8.5) South Asia will experience heat waves that “exceed the survivability threshold” (sic!) from 2070 onwards. Researchers at MIT conclude in a 2017 study that 4% of the South Asia-population, about 70 million people, would face heatwaves of humid heat that will kill even healthy people in the shade within hours. The wet bulb temperature (WTB) would reach 35°C, which means that the human body cannot cool itself and shuts down.
Three quarters (1.3 billion people) in South Asia would experience at least one heatwave before the end of the century with wet bulb temperatures of 31°C, conditions of ‘extreme danger’. To compare: In 2015 there was a severe episode in wich 30°C WTB was measured. This led to 3,500 deaths in South Asia. According to this article the largest hospital in Karachi was receiving 1 patient per minute and the morgue was overflowing.
Wet bulb temperatures currently rarely exceeds 31°C. 35°C WTB has never been measured yet.
Researchers of the Massuchusetts Institute of Technology (MIT) warn that if greenhouse gas emissions will not be curbed, large parts of the Persian Gulf could become uninhabitable at the end of this century. Once every decade heat waves might occur in which the combination of temperature and humidity (the so-called “wet bulb temperature”) will exceed the equivalent of 35 degrees Celsius at 100% humidity. If such conditions are sustained for several hours they become fatal to the human body.
The latest edition of the National Climate Assessment of the United States, a report written by over 300 scientist, warns that because of climate change millions of inhabitants of the United States will migrate inland. The U.S. is not prepared.
States from which people will leave are, according to the authors, amongst others Massachusetts, New Jersey and New York.
The report does not predict when the flows of migrants can be expected. The authors do conclude that communities are not acting sufficiently.