Global warming
Th e global average temperature is already rising. Temperature records compiled from weather station data since 1880 show that seventeen of the eighteen warmest years ever recorded occurred during this century. Th e warmest year on record was 2016, and it was the third record-setting year in a row. 21 A year earlier, in 2015, the total temperature increase since the preindustrial era passed the long-anticipated 1 degree Celsius mark. 22 We are experiencing global warming.
Visual evidence of global warming is readily evident from space. Th e extent of polar sea ice is decreasing, especially in the Arctic, 23 and, globally, glaciers are receding at unprecedented rates. 24 As the ice melts, it triggers one of many feedback loops that increase the pace of global warming.
19 NOAA Earth System Research Laboratory, “Trends in Atmospheric Carbon Dioxide,” Global
Greenhouse Gas Reference Network (2015). Online: http://www.esrl.noaa.gov/gmd/ccgg/trends /weekly.html (accessed December 30, 2015).
20 IPCC, “Carbon Dioxide: Projected Emissions and Concentrations,” IPCC Data Distribution Centre
(2014). Online: http://www.ipcc-data.org/observ/ddc_co2.html (accessed December 30, 2015).
21 NASA, “NASA, NOAA Data Show 2016 Warmest Year on Record Globally,” NASA Press Release
17-006 (2017). Online: https://www.nasa.gov/press-release/nasa-noaa-data-show-2016-warmest-year -on-record-globally (accessed July 26, 2017). “Global Climate Report – Annual 2017,” NOAA (2018). Online: https://www.ncdc.noaa.gov/sotc/global/201713 (accessed March 13, 2018).
22 NOAA, “July 2015 Was Warmest Month Ever Recorded for the Globe,” ScienceDaily (2015). Online:
http://www.sciencedaily.com/releases/2015/08/150820152817.htm (accessed August 20, 2016);
NASA Goddard Institute for Space Studies, “GISS Surface Temperature Analysis (GISTEMP)”
(2016). Online: http://data.giss.nasa.gov/gistemp/ (accessed January 20, 2016).
23 NASA Earth Observatory, “Arctic Sea Ice.” Online: http://earthobservatory.nasa.gov/Features
/WorldOfChange/sea_ice.php (accessed December 30, 2015); NASA Goddard Space Flight Center,
“Global Sea Ice Diminishing, Despite Antarctic Gains,” ScienceDaily (2015). Online: http://www .sciencedaily.com/releases/2015/02/150210160103.htm (accessed December 30, 2015); Claire Parkinson , “ Global Sea Ice Coverage from Satellite Data ,” Journal of Climate 27 . 24 ( 2014 ): 9377 .
24 National Snow & Ice Data Center, “Global Glacier Recession” (2015). Online: https://nsidc.org
/glims/glaciermelt/ (accessed December 30, 2015); Michael Zemp et al., “ Historically Unprecedented Global Glacier Decline in the Early 21st Century ,” Journal of Glaciology 61 . 228 ( 2015 ): 745–62 .
Feedback loops
One oft en hears that our climate has passed a “tipping point” or, as one of the editors of this volume is fond of saying, is “coming apart at the seams.” Th ese are apt observations, as there are a myriad of feedback loops that drive the warming to proceed at an ever-increasing pace.
Th e warming is most pronounced in the northern polar regions where temperatures are rising twice as fast as they are at more temperate latitudes. Th is rapid warming is driven by a multiplicity of feedback loops that, collectively, are referred to as Arctic amplifi cation. 25 Th e primary feedback mechanism is the loss of ice and snow cover, which reduces the amount of sunlight refl ected back into space. Exposed land and water absorb more sunlight than did the ice and snow, and therefore accelerate the warming.
Black carbon—that is, soot—also exacerbates the warming. When soot settles on glaciers, it greatly reduces the refl ection of sunlight and increases its absorption. Th is warms the ice, which leads to more rapid melting and faster warming. Some of the soot eventually fl ows with the ice melt into the ocean. Once there, it dissolves, forming carbon dioxide that is released into the air where it further enhances greenhouse warming. 26
Th awing tundra adds to Arctic amplifi cation. In its normal state, tundra is permanently frozen soil that serves as a deep freeze for keeping carbon out of the atmosphere. In a warming climate, the tundra melts, forming pools of water beneath which vegetation decomposes. Decomposition underwater—in the absence of oxygen—produces carbon dioxide 27 and methane 28 that is subsequently released to the atmosphere. Th e methane is a major concern since it traps thirty times more heat than does an equivalent amount of carbon dioxide (over a hundred-year period). 29
Additional feedback loops come from the responses of biota to the warming climate, sometimes in unexpected ways. Tree growth, for example, is enhanced by excess carbon dioxide in the atmosphere. In principle, this should increase the number and extent of trees and hence increase the amount of carbon dioxide that is removed
25 NASA Earth Observatory. Online: http://earthobservatory.nasa.gov/IOTD/view.php?id=81214
(accessed December 30, 2015); M. Serreze and R. Barry , “ Processes and Impacts of Arctic Amplifi cation ,” Global and Planetary Change 77 . 1–2 ( 2011 ): 85–96 .
26 University of Georgia, “Climate Change Likely to Increase Black Carbon Input to the Arctic Ocean,”
ScienceDaily (2015). Online: http://www.sciencedaily.com/releases/2015/11/151130182247.htm (accessed December 1, 2015); Aron Stubbins et al., “Utilizing Colored Dissolved Organic Matter to Derive Dissolved Black Carbon Export by Arctic Rivers,” Frontiers in Earth Science (2015). Online:
http://dx.doi.org/10.3389/feart.2015.00063 (accessed December 1, 2015).
27 University of Colorado at Boulder, “Ancient Permafrost Quickly Transforms to Carbon Dioxide upon
Th aw,” ScienceDaily (2015). Online: http://www.sciencedaily.com/releases/2015/10/151026171407 .htm (accessed December 21, 2015); Travis Drake et al., “ Ancient Low-molecular-weight Organic Acids in Permafrost Fuel Rapid Carbon Dioxide Production upon Th aw ,” Proceedings of the National Academy of Sciences of the United States of America 112 . 45 ( 2015 ): 13946–51 .
28 National Snow and Ice Data Center, “Methane and Frozen Ground,” All about Frozen Ground
Online: https://nsidc.org/cryosphere/frozenground/methane.html (accessed December 30, 2015).
29 US EPA, “Overview of Greenhouse Gases.”
Prologue 15
from the atmosphere. However, destructive insects such as bark beetles and ash borers are thriving in the warmer climate and damaging or destroying entire forests of trees.
Th us, the ability of trees to absorb carbon dioxide is actually being severely reduced 30 or eliminated altogether. 31
Vegetation on land 32 and phytoplankton in the ocean 33 are responding to warmer temperatures in ways that reduce their net uptake of carbon dioxide. Although their rates of daytime photosynthesis (which removes carbon dioxide from the atmosphere) are increasing, their rates of nighttime respiration (which returns carbon dioxide to the atmosphere) are increasing even faster. Th e result is a net decrease in the uptake of carbon dioxide and a net decrease in the production of oxygen. Not only does this exacerbate global warming, it may ultimately threaten the availability of oxygen for higher-order species (like us) to breathe. Th is frightening possibility may be mitigated by the fact that plankton reproduce rapidly and thus might quickly evolve in ways that increase their ability to thrive and take in larger amounts of carbon dioxide. 34 Th e bottom line is that the prognosis is unclear: there are far too many species of plankton,
30 University of Wisconsin-Madison, “Munching Bugs Th wart Eager Trees, Reducing the Carbon Sink,”
ScienceDaily (2015). Online: http://www.sciencedaily.com/releases/2015/03/150302121609.htm (accessed March 4, 2015); J.J. Couture , T. Meehan , E. Kruger , and R. Lindroth , “ Insect Herbivory Alters Impact of Atmospheric Change on Northern Temperate Forests ,” Nature Plants 1 . 3 ( 2015 ): 15016 .
31 US National Parks Service, “Forest Health: Mountain Pine Beetle.” Online: http://www.nps.gov
/romo/learn/nature/mtn_pine_beetle_background.htm (accessed December 31, 2015); USDA Forest Service “Mountain Pine Beetle Epidemic.” Online: http://www.fs.usda.gov/detail/mbr /home/?cid=stelprdb5139168 (accessed December 31, 2015); Ryan DeSantis et al., “ Eff ects of Climate on Emerald Ash Borer Mortality and the Potential for Ash Survival in North America ,”
Agricultural and Forest Meteorology 178–9 ( 2013 ): 120–8 .
32 Umeå University, “Increased CO 2 Concentrations in the Atmosphere Have Altered Photosynthesis
of Plants over the 20th Century,” ScienceDaily (2015). Online: http://www.sciencedaily.com /releases/2015/12/151207164333.htm (accessed December 9, 2015); Ina Ehlers et al., “ Detecting Long-term Metabolic Shift s Using Isotopomers ,” Proceedings of the National Academy of Sciences of the United States of America 112 . 51 ( 2015 ): 15585–90 ; Princeton University, “Warm Nights Could Flood the Atmosphere with Carbon under Climate Change,” ScienceDaily (2015). Online: http://
www.sciencedaily.com/releases/2015/12/151207165741.htm (accessed December 9, 2015); William Anderegg et al., “ Tropical Nighttime Warming as a Dominant Driver of Variability in the Terrestrial Carbon Sink ,” Proceedings of the National Academy of Sciences of the United States of America 112 . 51 ( 2015 ): 15591–6 .
33 University of Leicester, “Failing Phytoplankton, Failing Oxygen,” ScienceDaily (2015). Online: http://
www.sciencedaily.com/releases/2015/12/151201094120.htm (accessed December 3, 2015); Yadigar Sekerci and Sergei Petrovskii , “ Mathematical Modelling of Plankton–Oxygen Dynamics under the Climate Change ,” Bulletin of Mathematical Biology 77 . 12 ( 2015 ): 2325–53 .
34 University of Hawaii at Manoa, “Rapidly Acidifying Waters Pose Major Th reat for
Southern Ocean Ecosystem,” ScienceDaily (2015). Online: http://www.sciencedaily.com /releases/2015/11/151102125452.htm (accessed November 2, 2015); Claudine Hauri , Tobias Friedrich , and Axel Timmermann , “ Abrupt Onset and Prolongation of Aragonite Undersaturation Events in the Southern Ocean ,” Nature Climate Change 6 ( 2015 ): 172–6 ; University of Exeter, “Phytoplankton Like It Hot,” ScienceDaily (2015). Online: http://www.sciencedaily.com/releases/2015/12/151217151533.
htm (accessed December 19, 2015); Gabriel Yvon-Durocher et al., “ Five Years of Experimental Warming Increases the Biodiversity and Productivity of Phytoplankton ,” PLOS Biology 13 . 12 ( 2015 ):
e100232 ; University of Exeter, “Don’t Forget Plankton in Climate Change Models, Says Study,”
ScienceDaily (2015). Online: http://www.sciencedaily.com/releases/2015/11/151127102337.htm (accessed December 19, 2015); Daniel Padfi eld et al., “ Rapid Evolution of Metabolic Traits Explains Th ermal Adaptation in Phytoplankton ,” Ecology Letters 19 ( 2015 ): 133–42 .
each of which may respond diff erently in diff erent conditions, to know what the future will actually hold. 35
Many other feedback loops and phenomena, each of which accelerates global warming, have been discovered. For example:
● Microbial activity in soils, which releases carbon dioxide, is increasing. 36
● Th e extinction of large fruit-eating animals in tropical forests leads to a loss of trees since those animals are no longer available to spread tree seeds in their excrement. 37
● Shift ing global wind patterns and deep ocean currents are driving warm air and water toward the poles where it accelerates the rate of ice melting. As the ice melts, cracks form that allow warm water to penetrate and fl ow under glacial interiors thus melting them even faster. 38
● Freshwater lakes are warming even faster than are the oceans and atmosphere, leading to algal blooms that increase methane emissions. 39
It would be comforting to fi nd an equal number of feedback loops and phenomena that act to slow down the rate of global warming. Unfortunately, the fact of the matter is that the vast majority of results point to accelerated warming; it is rare to fi nd a new research result that points to a slowing of the warming. Th is disturbing trend leads to the intuitive (although not rigorously scientifi c) conclusion that the current models are underestimating the actual rate of warming. In addition, the fact that we have never before observed global warming of this magnitude leads to the intuitive (and, again, not rigorously scientifi c) worry that there may be many more feedback loops of which we are currently unaware precisely because we have never before seen warming of this magnitude. In short, although we can make educated inferences about the future, there is a disturbing sense that those inferences might well be grievously understated.
37 University of East Anglia, “Extinction of Large Animals Could Make Climate Change Worse,”
ScienceDaily (2015). Online: http://www.sciencedaily.com/releases/2015/12/151218161237.htm
39 Washington State University, “Climate Change Rapidly Warming World’s Lakes: More than Half
World’s Freshwater Supplies Measured,” ScienceDaily (2015). Online: http:/www.sciencedaily.com /releases/2015/12/151216174555.htm (accessed December 20, 2015); C.M. O’Reilly et al., “ Rapid and Highly Variable Warming of Lake Surface Waters around the Globe ,” Geophysical Research Letters 42 . 24 ( 2015 ): 10,773–81 .
35 Mike Vogt , “ Adrift in an Ocean of Change ,” Science 350 . 6267 ( 2015 ): 1466–8 .
36 Princeton University, “Dirty Pool: Soil’s Large Carbon Stores Could Be Freed by
Increased CO 2 , Plant Growth,” ScienceDaily (2014). Online: http://www.sciencedaily.com/
releases/2014/12/141223114233.htm (accessed December 24, 2014); Benjamin Sulman et al.,
“ Microbe-driven Turnover Off sets Mineral-mediated Storage of Soil Carbon under Elevated CO 2 ,”
Nature Climate Change 4 . 12 ( 2014 ): 1099 .
Prologue 17
Observations of the actual rate of global warming corroborate the sense that matters are getting seriously out of hand: the current rate of warming is signifi cantly faster than it has been any time in the past, 40 and the impacts of this warming are very clearly already upon us.