Strongest climate signals coming from Arctic and extreme weather events
By Bob Berwyn
FRISCO — Some of the most compelling signs of global warming impacts continued to come from the Arctic in 2012, where sea ice extent reached a record low and Greenland experienced record surface melting last summer.
Another worrying sign is the warming in permafrost regions, where significant thawing could release a new surge of heat-trapping greenhouse gases that would intensify warming.
The average global temperature for the year was among the top-10 warmest on record, and other climate observations also are consistent with what to expect in a warming world, according to climate experts who released the 2012 State of the Climate report this week.
“It’s really important to take a look at broad spectrum of measurements we have available,” said Tom Karl, director of NOAA’s National Climatic Data Center. “In 2012 not every variable broke a record, but there were some notable indicators,” Karl said, listing record sea level rise, temperature records in permafrost regions and stratospheric temperature records.
That broader look shows a wide range of signals consistent with increasing temperatures and signals persistence of warmer conditions, not just a one-time or short-term temperature anomaly. Some of those signs include record-low spring snow cover. 2012 marked the third time in the last five years with record-low June snow cover, which is declining at the rate of 17 percent per decade in the northern hemisphere. Lake ice is also melting sooner, anywhere from a few weeks to a month earlier
“Many of the events that made 2012 such an interesting year are part of the long-term trends we see in a changing and varying climate,” said acting NOAA Administrator Dr. Kathryn D. Sullivan.
A short Q&A with Dr. Kevin Trenberth, head of the Climate Analysis Section at the USA National Center for Atmospheric Research on the State of the Climate report:
Q: How does 2012 fit into the global temperature trends of the past couple of decades?
Trenberth: It is quite consistent with the overall warming we expect from human-induced climate change. The warmth in the US was exceptional, with the major drought, heat waves and wild fires. The hot spots tend to move around and last year it was the US. This year it was Australia in January and several places have experienced major heat waves the northern summer: The US (but not like last year), Siberia, China, and even Europe. In 2009 it was Australia, in 2010 it was Russia, in 2011 it was Texas and Oklahoma, etc. These increases in extremes are what cause problems by breaking records, going outside of previous experience, and increasing risk of wildfires and poor air quality. At the same time, in other spots there have been extremes of rainfall and flooding.
Q: What can we expect the next 10 years? Are temperatures going to spike to new records with the next El Niño?
Trenberth: For the global mean, very likely. We seem to be in a pattern where global temperatures are not increasing at the same rates as earlier, and this relates to decadal variations especially in the Pacific, with more heat being deposited at ocean depths. So the ocean is warming up and Arctic sea ice has been at record low levels. 2012 was the al- time record in minimum summer sea ice. 2013 is low, but not that low, but odds are good that the 2012 record will be broken as we head toward an ice free Arctic by about 2030.
Q: What are we learning about ocean heat content?
Trenberth: It is more complicated than previously thought. Some heat is penetrating into greater depths, below 700 meters, than expected, but OHC reflects the overall energy imbalance at the top of atmosphere: over 90 percent of the heat goes into the ocean. Some gets stored and can come back in El Niño events, but some just warms the ocean helping it to keep up with the overall warming of the planet. The fact that this is occurring faster than previously thought means climate change effects in the longer term (centuries) could be bigger and occur sooner.
Q: Is there increasing evidence for links between global warming and extreme weather? What is the most compelling evidence?
Trenberth: Yes. That is where the biggest impacts occur. The main evidence is the breaking of records in ways consistent with a warming planet: high temperature records (heat waves), drought intensity, wild fires, sea ice loss, glacier loss, stronger storms, heavier rains, risk of flooding. Whether a heavy rain causes flooding in a region depends a lot on the local infrastructure and drainage systems, which varies around the world.
Trenberth also explained the significance of increasing stratospheric warmth:
With increasing CO2, surface temperatures go up but stratospheric temperatures go down: The atmosphere is trapping heat and the greenhouse gases, including CO2, are what radiate both up and down. At some level that radiation causes cooling — It always causes cooling but is offset by the increase in upward radiation from below. By contrast, if the sun were a cause (of global warming) the surface and stratosphere would both be warming. So stratospheric cooling is a CO2 signature.
More highlights from the report:
- Warm temperature trends continue near Earth’s surface: Four major independent datasets show 2012 was among the 10 warmest years on record, ranking either 8th or 9th, depending upon the dataset used. The United States and Argentina had their warmest year on record.
- La Niña dissipates into neutral conditions: A weak La Niña dissipated during spring 2012 and, for the first time in several years, neither El Niño nor La Niña, which can dominate regional weather and climate conditions around the globe, prevailed for the majority of the year.
- The Arctic continues to warm; sea ice extent reaches record low: The Arctic continued to warm at about twice the rate compared with lower latitudes.Minimum Arctic sea ice extent in September and Northern Hemisphere snow cover extent in June each reached new record lows. Arctic sea ice minimum extent (1.32 million square miles, September 16) was the lowest of the satellite era. This is 18 percent lower than the previous record low extent of 1.61 million square miles that occurred in 2007 and 54 percent lower than the record high minimum ice extent of 2.90 million square miles that occurred in 1980. The temperature of permafrost, or permanently frozen land, reached record-high values in northernmost Alaska. A new melt extent record occurred July 11-12 on the Greenland ice sheet when 97 percent of the ice sheet showed some form of melt, four times greater than the average melt this time of year.
- Antarctica sea ice extent reaches record high: The Antarctic maximum sea ice extent reached a record high of 7.51 million square miles on September 26. This is 0.5 percent higher than the previous record high extent of 7.47 million square miles that occurred in 2006 and seven percent higher than the record low maximum sea ice extent of 6.96 million square miles that occurred in 1986.
- Sea surface temperatures increase: Four independent datasets indicate that the globally averaged sea surface temperature for 2012 was among the 11 warmest on record. After a 30-year period from 1970 to 1999 of rising global sea surface temperatures, the period 2000-2012 exhibited little trend. Part of this difference is linked to the prevalence of La Niña-like conditions during the 21st century, which typically lead to lower global sea surface temperatures.
- Ocean heat content remains near record levels: Heat content in the upper 2,300 feet, or a little less than one-half mile, of the ocean remained near record high levels in 2012. Overall increases from 2011 to 2012 occurred between depths of 2,300 to 6,600 feet and even in the deep ocean.
- Sea level reaches record high: Following sharp decreases in global sea level in the first half of 2011 that were linked to the effects of La Niña, sea levels rebounded to reach record highs in 2012. Globally, sea level has been increasing at an average rate of 3.2 ± 0.4 mm per year over the past two decades.
- Ocean salinity trends continue: Continuing a trend that began in 2004, oceans were saltier than average in areas of high evaporation, including the central tropical North Pacific, and fresher than average in areas of high precipitation, including the north central Indian Ocean, suggesting that precipitation is increasing in already rainy areas and evaporation is intensifying in drier locations.
- Tropical cyclones near average: Global tropical cyclone activity during 2012 was near average, with a total of 84 storms, compared with the 1981-2010 average of 89. Similar to 2010 and 2011, the North Atlantic was the only hurricane basin that experienced above-normal activity.
- Greenhouse gases climb: Major greenhouse gas concentrations, including carbon dioxide, methane, and nitrous oxide, continued to rise during 2012. Following a slight decline in manmade emissions associated with the global economic downturn, global CO2 emissions from fossil fuel combustion and cement production reached a record high in 2011 of 9.5 ± 0.5 petagrams (1,000,000,000,000,000 grams) of carbon , and a new record of 9.7 ± 0.5 petagrams of carbon is estimated for 2012. Atmospheric CO2 concentrations increased by 2.1 ppm in 2012, reaching a global average of 392.6 ppm for the year. In spring 2012, for the first time, the atmospheric CO2 concentration exceeded 400 ppm at several Arctic observational sites.
- Cool temperature trends continue in Earth’s lower stratosphere: The average lower stratospheric temperature, about six to ten miles above the Earth’s surface, for 2012 was record to near-record cold, depending on the dataset. Increasing greenhouse gases and decline of stratospheric ozone tend to cool the stratosphere while warming the planet near-surface layers.
The 2012 State of the Climate report is peer-reviewed and published annually as a special supplement to the Bulletin of the American Meteorological Society. This year marks the 23rd edition of the report, which is part of the suite of climate services NOAA provides to government, the business sector, academia, and the public to support informed decision-making. The full report can be viewed by visiting http://www.ncdc.noaa.gov/bams-state-of-the-climate/2012.php
Filed under: Arctic, climate and weather, El Niño, Environment, global warming, La Niña Tagged: | 2012 state of the climate report, American Meteorological Society, climate change, global warming, National Climatic Data Center