So far, we’ve looked at land temperatures and ocean temperatures separately. Here’s a graph which combines both the earth’s land and ocean temperatures dating back to 1880.
Figure 3-9 Temperature Time-Series for land-only, ocean-only, and combined land-and-ocean
According to NASA, in 2016 the Earth’s surface temperature averaged 1.789°F (.993C) warmer than the mid-20th century baseline. This is the warmest recorded temperature since record keeping began in 1880 and the third year in a row to set a new record.
The earth’s temperature in 2014 was 1.03°C (1.854°F) above the 20th century average, and over the past 134 years, according to the IPCC, the earth’s temperature has risen 0.85°C (1.53°F).
https://www.nasa.gov/press-release/nasa-noaa-data-show-2016-warmest-year-on-record-globally NASA RELEASE 17-006 Jan 18, 2017
Acidification of the Oceans
The oceans not only hold heat, but also serve as major reservoirs for carbon, absorbing somewhere between one-quarter and one-third of the CO2 humans emit each year. https://www.pmel.noaa.gov/co2/story/Ocean+Acidification
pH measures acidity, which is the concentration of hydrogen ions. According to NOAA, the pH of the ocean’s surface is 30% more acidic now than it was at the beginning of the Industrial Revolution. If we continue at a business-as-usual pace, NOAA scientists predict that by 2100 the ocean will be 150 percent more acidic resulting in a pH that the oceans haven’t experienced in more than 20 million years.
https://www.pmel.noaa.gov/co2/story/Ocean+Acidification
https://www.epa.gov/ocean-acidification/effects-ocean-and-coastal-acidification-ecosystems
The adverse effects of acidification of ocean ecosystems are already significant and business-as-usual scenarios predict a future with even greater negative effects.
The most well-known effect of ocean acidification is its devastating effect on coral reefs. As of October 2016, 40% of the world’s coral have already been lost.
How a healthy reef (left) in American Samoa bleached (Centre) and eventually died during the current bleaching event
Coral reefs provide habitat for a great diversity of sea life. Twenty-five percent of all marine life and more than 4,000 species of fish depend upon coral reefs for their survival.
The image on the left shows the bleaching of a coral reef at Lizard Island on the Great Barrier Reef. The image on the right, clicked two months later, shows the reef dead.
Studies by a range of groups have come to the same conclusion. If the earth continues to warm, we will witness massive coral losses.
The World Resource Institute’s Annual Reviews estimates that about 90 percent of the coral species in the world will be in danger of bleaching by 2030. The study, published in July 2016 suggests coral bleaching will become an annual event after 2039. A study in the journal, Global Change Biology, and another by scientists in Australia concluded that the overall suitability of our oceans to support coral reefs will be considerably reduced in the future.
In addition to the ecological cost of ocean acidification, coral reefs are the basis for many marine ecosystems that provide food for humans. in the form of fish and other seafood with an estimated economic value of $30 billion dollars a year. The total economic value of coral reefs has been estimated to be over 800 billion dollars.
The loss of coral reefs is a loss of tens of billions of dollars a year with a value estimated to be 18% of the world’s GDP in 2100 (Markarow et al., 2009).
Storms
On October 22, 2015, Patricia was a weak tropical storm. A day later it was a Category 5 hurricane, the fastest strengthening storm ever recorded and the strongest ever recorded in the Western Hemisphere. Patricia broke the record for the lowest barometric pressure (882 mb). Its winds reached 200 mph, the second highest sustained windspeed ever recorded. Typhoon Nancy had recorded sustained wind speeds of 215 mph in 1961.
(Figure 3-10) Patricia as a Category 5 with maximum sustained winds of 200 mph on October 23, 2015 morning. (NASA)
Hurricane Patricia was the 4th most devastating storm in the Pacific in four years. One of them, Typhoon Haiyan, had gusts to 235 mph and devastated the Philippines. These storms are not unique. The world is experiencing stronger storms and more storms in unique locations. Here in the US, we have seen catastrophic damage to life and property from Hurricanes Katrina and Sandy. In 2004, Brazil was struck by its first ever hurricane. In the same decade, the Canary Islands, Spain and Myanmar were struck by their first recorded tropical storms.
You’ll recall that the laws of thermodynamics tell us that heat moves from warm temperatures to cool temperatures. Tropical storms are heat engines, driven by the difference in temperatures between the warm ocean and the cooler land. From a physics perspective, they serve to dissipate heat that has built up in the oceans during the summer when the oceans are at their warmest and the atmosphere is beginning to cool toward winter. The heat in the warmer ocean water flows to the cooler atmosphere, and tropical storms and hurricanes are efficient mechanisms for this transfer of energy.
This thermodynamic fact is consistent with the phenomenon we have observed that Hurricane Intensity generally Increases with Rising Sea Surface Temperatures
(Figure 3-11) Observed Sea surface temperature (blue) and the Power Distribution Index (green)
The Power Dissipation Index, measures the duration and intensity of wind speed and rainfall both of which are indicators of energy transfer and research has found that since the mid-1970s, there has been an increase in the energy of storms.
A report called, “A trade-off between intensity and frequency of global tropical cyclones” by Nam-Young Kang and James B. Elsner in the journal, Nature and Climate Change (May 2015), theorizes that the increased yearly energy in the ocean translates into either more, less intense storms, or fewer, more intense storms.
In their study, the authors report that between 1983 and 2012, wind speeds in tropical cyclones increased by 3 mph and there were 6.1 fewer storms than they would expect if ocean and land temperatures had not increased.
The largest storms are becoming more intense and, with higher wind speeds, more destructive. They last longer and make landfall more frequently than in the past. Because this phenomenon is strongly associated with sea surface temperatures, it is reasonable to suggest that the increased intensity of storms we are observing is directly related to the warming trends we have observed.
More intense hurricanes are not the only change in our weather we’re observing. “Weather records show that storms with extreme precipitation have become more frequent over the last 60 years.”
(Figure 3-12) Cooperative institute for Climate and Satellites
Warmer temperatures provide more energy for the hydrologic cycle. More evaporation puts more moisture into the atmosphere. More moisture means more precipitation, and that is what has been observed. The following chart shows the changes in extreme precipitation events. As you can see, they are most pronounced in the Northeast and Great Lakes regions.
In the Great Lakes region, as much as half the annual total precipitation falls during ten days of the year. In many locations, the amount of precipitation has increased 20-30% between 1971-2000.
Amount of Precipitation Falling in the Heaviest 1% of Storms
(Figure 3-13 Percent increases in the amount falling in the heaviest 1% of daily precipitation events from 1958 to 2012. Trends toward more intense precipitation are particularly clear in the Midwestern and Northeastern US.
According to the IPCC,
Averaged over the mid-latitude land areas of the Northern Hemisphere, precipitation has increased since 1901 (medium confidence before and high confidence after 1951). For other latitudes, area-averaged long-term positive or negative trends have low confidence. Observations of changes in ocean surface salinity also provide indirect evidence for changes in the global water cycle over the ocean (medium confidence). It is very likely that regions of high salinity, where evaporation dominates, have become more saline, while regions of low salinity, where precipitation dominates, have become fresher since the 1950s. {1.1.1, 1.1.2}
The distribution of the intensity of precipitation events has also changed, so that more precipitation is falling during heavier storms. These effects – the clustering of precipitation into heavier storms and the polarization of wet and dry seasons – can increase the probability of both extreme precipitation and of prolonged dry periods by extending the time between rainfalls.
What about Drought in the U.S.?
As the planet warms, the paths of storms change causing arid areas to grow in size. The increased rainfall in some places means less in others. Arid areas grow in size because of the changing patterns of air circulation.
As temperatures have warmed over the past century, the prevalence and duration of drought has increased in many places. The American West is one such place.
Figure 3-14 Areas of Abnormally Dry to Exceptional Drought in the United States.
According the Weekly U.S. Drought Monitor, about 26.2 percent of the contiguous US and about 21.9 percent of the US including Alaska, Hawaii and Puerto Rico was classified as experiencing moderate to exceptional (D1-D4) drought at the end of October 2015.
Glaciers
A glacier is a large mass of ice flowing very slowly through a valley or spreading outward from a center. Glacier’s form over many years from packed snow in areas where snow accumulates faster than it melts.
Glaciers occur in Alpine regions, the Arctic, and the Antarctic over land and frozen ocean. When temperatures warm, as discussed in the previous section, less snow falls and the leading edge of the glacier melts. A glacier is always moving, but when its forward edge melts faster than the ice behind it advances, the glacier as a whole shrink backward. Today, glaciers around the world are retreating giving further evidence of the global warming trend.
Hassan Basagic a geologist at Portland State University quantified the surface area change of fourteen glaciers throughout the Sierra Nevada mountains determining that glaciers had lost an average of 55 percent of their surface area between 1900 and 2004.
Here are some photographs of glaciers from around the world. The first comes from the same Sierra Nevada mountains we saw in satellite pictures in figure 3
Darwin Glacier, Kings Canyon National Park, California
The following photographs are an example of what is happening today in California and alpine glaciers around the world.
Fig 3-17:
Darwin Glacier August 14, 1908 Darwin Glacier September 25, 2010. photo. Gilbert
Muir Glacier, Glacier Bay National Park and Preserve, Alaska
Fig. 3-18: Image Credit: National Snow and Ice Data Center, W. O. Field, B. F. Molnia
On the left is a photograph of Muir Glacier in Alaska taken on August 13, 1941 by glaciologist William O. Field. On the right is a photograph taken from the same vantage point on August 31, 2004 by geologist Bruce F. Molnia of the United States Geological Survey (USGS). According to Molnia, between 1941 and 2004, the glacier retreated more than twelve kilometers (seven miles) and thinned by more than 800 meters (almost half a mile). Ocean water has filled the valley, replacing the ice of Muir Glacier and the end of the glacier has retreated out of the field of view.
The glacier’s absence reveals scars where glacier ice once scraped high up against the hillside. In 2004, trees and shrubs grew thickly in the foreground. In 1941, there was only bare rock. This plant growth is a good example of the first stage of succession we discussed earlier in the series.
New habitat with niches for colonizer species is now available after rock covered with ice for thousands, in some cases, millions of years is exposed.
What about Snow and Ice?
There is another climate-related change causing drought.
If temperatures are rising, then we should expect to see evidence of a decrease in the amount of snow and ice recorded in colder climates. That is exactly what we are observing in the Western US. With warmer weather comes less snowfall and earlier, smaller snow melt. For both of these reasons, the United States Southwest, dependent for 30% of its water from that snowmelt, is considered one of the most likely places for drought to occur.
Much of the water supplied to both urban and farming areas comes from melting glaciers in the Sierra Nevada mountains. A recent study of tree-ring data suggests that 2015 record low snowpack levels in the Sierra Nevada’s are unprecedented and that that current snowpack low has a strong likelihood of occurring only once every 500 years and only once every 1,000 years below 7,000 feet. (We’ll discuss more about tree-ring data later in this series.)
Figure 3-15 Sierra Nevada Snowpack changes over 5 years
These two photographs in figure 3-15 above show the decrease in snowpack over the past five years. Similar observations are being made in many other areas around the world.
3-16 Snowpack potential throughout the world. Reddest areas are highest risk; yellow, lowest. Blue/white areas, future rainfall should be sufficient to supply present human needs; Gray regions indicate basins where rainfall might be insufficient, potentially making them dependent on snow or other sources.
(Mankin et al., Environmental Research Letters 2015)
Figure 3-16 shows those areas in the world where there is a “decreased potential” for snowpack and the water it supplies when it melts.
About 15% of the earth’s oceans are covered with ice. This ice is made up of ‘new ice’, which ice formed in the most recent winter, and ‘old ice’, which is more than one year old. The amount of new ice is highly dependent upon the weather which varies from year to year. Old ice tends to be thicker, more representative of climate, and therefore, for this discussion a more important measure. The following chart examines Arctic ice coverage (surface area) from 1952-2009.
Fig. 3-22: Source: Rayner et.al, 2004, updated
This graph shows a clear trend of diminishing ice cover over the past 60 years. The next chart looks at the volume of Arctic ice.
(figure 3-23) Source: Polar Science Centre, University of Washington
The total amount of Arctic ice has been diminishing by about 3% per decade and is certainly consistent with the conditions of a warming planet.
Next week we’ll discuss land and ice in more detail!
photo by Wes Golomb
