This week we’ll be talking more about Climate Change and its impact over the years on the planet.
Was there an update from 2019?
The 2010’s was the hottest decade on record, the last 5 years of the 2010’s was the hottest five years on record, and each of the past five decades has been warmer than the previous. Here is NASA’s chart of the ten warmest years since 1880.
Table 3-4 compares the ratios of record high to record low temperatures by decade. In a stable climate we would expect to see a similar number of record high and low temperatures which is, indeed what the data showed for the 1950’s.
Figure 3-4: 60 Year Ratio of High temperature to Low Temperature
“The relative increase of record high maximum temperatures compared to record low minimum temperatures in the U.S.”
As you can see, the ratio of record highs to lows has been steadily changing and by the period 2000-2009, there were more than double the number of record high temperatures to low temperatures.
Figure 3-5: Global Land and Ocean Temperature Anomalies From June-August. Authors: Gerald A. Meehl, Claudia Tebaldi, Guy Walton, David Easterling, and Larry McD
Here is a list of some of the specific events that occurred in 2019:
Here is another chart of world surface (land) temperatures from 1980-2006.
Fig 3-5 Surface Temperature Record
Global surface temperature change for the period 1980-2004. The blue line is the monthly average, the black line is the annual average and the red line is the 5-year running
Though this graph shows fundamentally the same information as the previous graphs, it is interesting to note the drop in the earth’s temperature for several years following the 1991 eruption of Mt. Pinatubo in the Philippines, the second largest volcanic eruption of the 20th century. Also interesting to note is that at the time of the Pinatubo eruption, the existing climate models successfully predicted what would happen – a several year drop in temperature followed by rising temperatures.
This is the first time we were able to confirm a climate model using a volcanic eruption as a test case. It is certainly not the first time we have observed a volcanic eruption affecting the weather.
According to an article in Live Science, written by Wynne Perry, the ‘Little Ice Age’ – a cold period during which the Thames River in England and canals in Holland froze – began in the late 13th century at a time of the eruptions of mount Krakatau and lasted through the late 19th century.
On April 10, 1815, Mount Tambora erupted in Indonesia.
Global temperatures dropped by about five degrees and 1816 became known as the “year without a summer.” In May of 1883, Krakatoa erupted with an estimated force of 200 megatons of TNT. The shock wave from the explosion put 11 cubic miles of debris into the atmosphere. Average global temperature dropped by 1.2 degrees for the next five years.
Recent research suggests that volcanic eruptions have the effect of cooling the oceans. A study by Peter Gleckler of the Lawrence Livermore National Laboratory found that the ash injected into the atmosphere by volcanoes may block out sunlight for years which cools ocean surface waters. (Nature, vol 439, p 675).
If the ocean was indeed cooled by these volcanic eruptions as Gleckler suggests, this suggests that these eruptions may be slowing the course of climate change a bit. The earth’s average temperature has risen about 0.65°C (1.17°F) since the start of the 20th century. This may not seem like much, but it is already affecting ecosystems.
Changes of a couple of degrees could adversely impact the Midwest breadbasket of the U.S and other fertile areas around the world.
“…the temperature increase that occurred between 1981 and 2002 reduced major cereal crop yields by an annual average of 40 million metric tons — losses worth $5 billion a year. Those losses are sobering, but nothing compared to what might be in store: A recent study sponsored by the Consultative Group on International Agricultural Research forecast a 51% decline in India’s wheat-growing land, potentially leaving hundreds of millions hungry. And, last week, China’s top meteorological official warned that global warming could cut the nation’s grain harvest by 5 to 10% by 2030. And all this will be happening while both countries add more mouths to feed.”
Furthermore, a couple degrees variance in ocean temperature could mean the destruction of a thriving coral reef ecosystem, one of the most diverse ecosystems in the world, which play host up to one-quarter of all marine species. According to the World Wildlife Federation,
“Coral reefs around the world have been severely damaged by unusually warm ocean temperatures.” They provide nurseries for many species of commercially important fish, protection of coastal areas from storm waves, and are a significant attraction for the tourism industry.
Coral reefs are very fragile sensitive ecosystems that can only tolerate a narrow temperature range. One of the most visually dramatic effects of climate change on corals has been bleaching. When the ocean warms, the heat affects the tiny algae which live symbiotically inside the corals and supply them with food. The heat stress damages the algae and in consequence leads to coral death. Global warming could now mean a death sentence for many coral reefs. If the present rate of destruction continues, most of the world’s coral reefs could be killed within our lifetime.
Ten thousand years ago, New Hampshire was covered with two miles of ice, and the average world temperature was 5 degrees cooler than now. How we know this, and so much more of what occurred prior to human record keeping is a fascinating detective story which we will consider shortly, but rather than get ahead of ourselves, let’s continue our discussion of human observation and measurement of climate change.
What’s the Story with Warming Oceans?
About two-thirds of the earth’s surface is water. One of the interesting properties of water is its ability to hold heat. Water is so good at this that we measure Heat Capacity – how much heat a substance can hold – by comparing it to water.
The world’s oceans are capable of storing enormous amounts of heat. Water does not warm and cool as fast as land, so changes are moderated, but they can be clearly measured. According to the IPCC,
“Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high confidence) with only about 1% stored in the atmosphere.”
Your mother may have taught you to run a jar under hot water when you are unable to open the lid. Why? Because the heat causes the metal lid to expand, making it easier to open. Any material, solid, liquid or gas, will take up more space as it warms due to higher energy levels (faster moving particles).
This is called Thermal Expansion.
When exposed to a warmer atmosphere, water absorbs some of the heat and its temperature rises. In turn, warming water expands, causing sea levels to rise. The warming also melts glaciers and the water which melts over land runs off into the ocean, causing sea levels to rise further.
What follows are the results of several different investigations into the temperature of the oceans. This data is reflected in the following three graphs of ocean temperatures giving us a measure of ocean temperature dating back to 1880.
Why is the Global Upper Ocean Heat Content Rising?
Figure 3-6 shows the heat content of the ocean. The dots represent seasons of specific years, and the black line represents range of the heat content. This graph show an unmistakable warming trend since the late 1960’s.
Fig. 3-6: Time series of seasonal (red dots) and annual average (black line) of global upper ocean heat content for the 0-700m layer since 195r.
While ocean heat content varies significantly from place to place and from year to year as a result of changing ocean currents and natural variability, reliable measurements of the period show a strong trend. Increasing heat content in the ocean is also consistent with sea level rise, which is occurring mostly as a result of thermal expansion of the ocean water as it warms. (Sato and Hansen, 2010)
Figure 3-7 looks at the same question from a different perspective. Instead of measuring heat content, the next graph measures the amount of change in sea level. Measuring the relative sea level, like relative temperature measurements, yields more accurate data for early measurements, prior to satelites.
Fig. 3-7: This Graph (Sato & Hansen, 2010) shows mean sea level rise over the past 140 years. (http://www.zeeburgnieuws.nl/nieuws/mb_sea_level_rise.html)
Global mean sea level has been rising at an average rate of approximately 1.7 mm/year over the past 100 years (measured from tide gauge observations), which is significantly larger than the average rate over the last several thousand years. Since 1993, global sea level (shown in green in the following chart) has risen at an even faster rate of around 3.5 mm/year. It is expected that melting land ice from Greenland and alpine glaciers will play a more significant role in contributing to future sea level rise.
Figure 3-8 looks at “Absolute Sea Level” using tide gauges as the measurement devices. As with temperature measurements, the margin of error is greater with early measurements and is reflected in the shaded area around the line.
Fig. 3-8: Trends in Global Average Sea Level 1870-2008
Each of these studies measured sea level in a different way. As you can see by the graphs, all three measurement approaches came to fundamentally the same conclusion. The oceans are warming and, as a result, sea level is rising.
According to NOAA In 2014, ”…the globally-averaged sea surface temperature was 1.03°F (0.57°C) above the 20th century average. This was the highest among all years in the 1880–2014 record, surpassing the previous records of 1998 and 2003 by 0.09°F (0.05°C)”.
So far, we’ve looked at land temperatures and ocean temperatures separately. Next week we’ll discuss annual temperatures and ocean acidification.
What did you learn from this week’s blog?
