fuels. Fifteen of the 16 hottest years on record have been in the 21st Century.5 Heat waves have become more frequent and intense, threatening human health, stressing water resources, and increasing energy demands.8 In 2016, record or near-record temperatures occurred in parts of the Middle East, North Africa, and Asia.5 The highest temperature observed was 129°F in Mitribah (Kuwait) in July 2016; this was the highest temperature on record for Asia.5 A late-season heat wave affected many parts of western and central Europe in 2016. For example, the temperature reached 113°F in Cordoba, Spain in September 2016.5 Precipitation. Drought and flooding are
both concerns. The hydrological cycle accelerates with global warming. As heat energy accumulates in the deep ocean, more water evaporates, causing increased intensity and frequency of precipitation. Evaporation from soil may also be increased, causing drought. Models indicate that, if climate change continues at the same pace, the future will see more heavy deluges (with flooding) and more frequent and longer droughts.5,8 In 2016, much of southern Africa began the year in severe drought. For the second year in a row, rainfall was 20-60% below average for the summer rainy season (October to April) in 2015/2016.5 2016 was also the driest on record over the Amazon Basin and there was significant drought in northeast Brazil, Central America, and northern South America.5
Conversely, China averaged its wettest year on record, with the annual mean rainfall 16% above the long-term average.5 Not surprisingly, the Yangtze basin in China experienced its most significant flood season since 1999, with some tributaries experiencing record flood levels.5 Lightning. Lightning results from the
amount of water or precipitation in the atmosphere and the instability of the atmosphere, a situation that allows air to rise rapidly. A 2014 study estimated that, for every average global increase of one degree Celsius, there would be a 12% increase in lightning.11 A significant increase in global temperatures (say, an average of three degrees Celsius) was estimated to
increase the number of lightning strikes by 50%.11 Half of all of the wildfires in the US are caused by lightning, so this could have a significant impact on the number of wildfires, especially in remote areas.
Ocean Health Since 1955, over 90% of the excess heat trapped by greenhouse gases has been stored in the oceans.1 The rest of this energy goes into melting sea ice, ice caps, and glaciers, and into warming the Earth’s land mass.12 A very small fraction of this thermal energy goes into warming the atmosphere.12 According to a 2017 study by Henson, et al., more than half of the world’s oceans could experience multiple symptoms of climate change over the next 15 years, including rising temperatures, acidification, lower oxygen levels, and decreasing food supplies.13 By mid-century, if there isn’t significant change in global warming, more than 80% of the oceans could be severely damaged.13 The Arctic, already among the most rapidly warming areas on Earth, may be one of the regions most severely affected.13 Ocean Temperature. Globally, average
sea surface temperatures in 2016 were the warmest on record.5 Global ocean heat content in 2016 was the second highest on record after 2015.5 It reached new record highs in the Northern Hemisphere in 2016.5 Warmer ocean temperatures pose several threats (e.g., rising sea levels), including destruction of coral reefs. For
example, during 2015–2016, record temperatures in Australia triggered a pan-tropical episode of coral bleaching, the third global-scale event since mass bleaching was first documented in the 1980s.14 The distinctive geographic footprints of recurrent bleaching on the Great Barrier Reef in 1998, 2002, and 2016 were determined by the spatial pattern of sea temperatures in each year.14 Water quality and fishing pressure had minimal effect on the unprecedented bleaching in 2016, which scientists concurred was almost solely related to ocean temperatures.14 Amount of Arctic Sea Ice. The seasonal maximum of sea ice in 2016 (14.52 million square kilometers in March), was the lowest in the 1979-2016 satellite record.5 The 2016 autumn freeze-up was exceptionally slow, with sea ice extent uncharacteristically contracting for a few days in mid-November.5 Sea Level Rise. Global sea levels rose
very strongly during the 2015/2016 El Niño, rising about 15 millimeters (mm) between November 2014 to a new record high in February 2016.5 This was well above the post-1993 trend of 3-3.5 mm per year.5
In order of importance, the sea level rise has been driven by: expansion of water volume as the ocean warms, melting of mountain glaciers in most regions of the world, and losses from the Greenland and Antarctic ice sheets.6 All of these factors are the result of a warming climate. The www.epi.umn.edu/mch z Spring 2017
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