Advanced Reading Practice: Climate Change: How Do We Know? (Optional)

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Climate Change: How Do We Know?

Earth's climate has changed throughout history. Just in the last 650,000 years, there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 11,700 years ago marking the beginning of the modern climate era — and of human civilization. Most of these climate changes are attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives.

Scientific evidence for warming of the climate system is unequivocal.

- Intergovernmental Panel on Climate Change

The current warming trend is of particular significance because most of it is extremely likely (greater than 95% probability) to be the result of human activity since the mid-20th century and proceeding at a rate that is unprecedented over decades to millennia.¹

Earth-orbiting satellites and other technological advances have enabled scientists to see the big picture, collecting many different types of information about our planet and its climate on a global scale. This body of data, collected over many years, reveals the signals of a changing climate.

The heat-trapping nature of carbon dioxide and other gases was demonstrated in the mid-19th century.² Their ability to affect the transfer of infrared energy through the atmosphere is the scientific basis of many instruments flown by NASA. There is no question that increased levels of greenhouse gases must cause Earth to warm in response.

Ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers show that Earth’s climate responds to changes in greenhouse gas levels. Ancient evidence can also be found in tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks. This ancient, or paleoclimate, evidence reveals that current warming is occurring roughly ten times faster than the average rate of ice-age-recovery warming. Carbon dioxide from human activity is increasing more than 250 times faster than it did from natural sources after the last Ice Age.³

The evidence for rapid climate change is compelling:

Global Temperature Rise

The planet's average surface temperature has risen about 2.05 degrees Fahrenheit (1.14 degrees Celsius) since the late 19th century, a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere.⁴  Most of the warming occurred in the past 40 years, with the six warmest years on record taking place since 2014. Not only was 2016 the warmest year on record, but eight months out of that year — from January through September, with the exception of June — were the warmest on record for those respective months. ⁵

Warming Oceans

The ocean has absorbed much of this increased heat, with the top 100 meters (about 328 feet) of ocean showing warming of more than 0.6 degrees Fahrenheit (0.33 degrees Celsius) since 1969.⁶ Earth stores 90% of the extra energy in the ocean.

Shrinking Ice Sheets

The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA's Gravity Recovery and Climate Experiment show Greenland lost an average of 279 billion tons of ice per year between 1993 and 2019, while Antarctica lost about 148 billion tons of ice per year.⁷

Glacial Retreat

Glaciers are retreating almost everywhere around the world — including in the Alps, Himalayas, Andes, Rockies, Alaska, and Africa.⁸

Decreased Snow Cover

Satellite observations reveal that the amount of spring snow cover in the Northern Hemisphere has decreased over the past five decades and the snow is melting earlier.⁹

Sea Level Rise

Global sea level rose about 8 inches (20 centimeters) in the last century. The rate in the last two decades, however, is nearly double that of the last century and accelerating slightly every year. ₁₀

Declining Arctic Sea Ice

Both the extent and thickness of Arctic sea ice has declined rapidly over the last several decades.¹¹

Extreme Events

The number of record high temperature events in the United States has been increasing, while the number of record low temperature events has been decreasing, since 1950. The U.S. has also witnessed increasing numbers of intense rainfall events. 12

Ocean Acidification

Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30%.^13,14 This increase is the result of humans emitting more carbon dioxide into the atmosphere and hence more being absorbed into the ocean. The ocean has absorbed between 20% and 30% of total anthropogenic carbon dioxide emissions in recent decades (7.2 to 10.8 billion metric tons per year).^15,16

 

References

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1. IPCC Fifth Assessment Report, Summary for PolicymakersB.D. Santer et.al., “ A search for human influences on the thermal structure of the atmosphere ,” Nature vol 382, 4 July 1996, 39-46
   Gabriele C. Hegerl, “ Detecting Greenhouse-Gas-Induced Climate Change with an Optimal Fingerprint Method ,” Journal of Climate, v. 9, October 1996, 2281-2306
   V. Ramaswamy et.al., “ Anthropogenic and Natural Influences in the Evolution of Lower Stratospheric Cooling ,” Science 311 (24 February 2006), 1138-1141
   B.D. Santer et.al., “ Contributions of Anthropogenic and Natural Forcing to Recent Tropopause Height Changes ,” Science vol. 301 (25 July 2003), 479-483.
2. In 1824, Joseph Fourier calculated that an Earth-sized planet, at our distance from the Sun, ought to be much colder. He suggested something in the atmosphere must be acting like an insulating blanket. In 1856, Eunice Foote discovered that blanket, showing that carbon dioxide and water vapor in Earth's atmosphere trap escaping infrared (heat) radiation.
   In the 1860s, physicist John Tyndall recognized Earth's natural greenhouse effect and suggested that slight changes in the atmospheric composition could bring about climatic variations. In 1896, a seminal paper by Swedish scientist Svante Arrhenius first predicted that changes in atmospheric carbon dioxide levels could substantially alter the surface temperature through the greenhouse effect.
   In 1938, Guy Callendar connected carbon dioxide increases in Earth’s atmosphere to global warming. In 1941, Milutin Milankovic linked ice ages to Earth’s orbital characteristics. Gilbert Plass formulated the Carbon Dioxide Theory of Climate Change in 1956.
3. Vostok ice core data; NOAA Mauna Loa CO 2 record
   Gaffney, O.; Steffen, W. (2017). " The Anthropocene equation ," The Anthropocene Review (Volume 4, Issue 1, April 2017), 53-61.
4. https://www.ncdc.noaa.gov/monitoring-references/faq/indicators.php
   https://crudata.uea.ac.uk/cru/data/temperature/​
   http://data.giss.nasa.gov/gistemp
5. https://www.giss.nasa.gov/research/news/20170118/
6. Levitus, S.; Antonov, J.; Boyer, T.; Baranova, O.; Garcia, H.; Locarnini, R.; Mishonov, A.; Reagan, J.; Seidov, D.; Yarosh, E.; Zweng, M. (2017). NCEI ocean heat content, temperature anomalies, salinity anomalies, thermosteric sea level anomalies, halosteric sea level anomalies, and total steric sea level anomalies from 1955 to present calculated from in situ oceanographic subsurface profile data (NCEI Accession 0164586). Version 4.4. NOAA National Centers for Environmental Information. Dataset. doi: 10.7289/V53F4MVP
   https://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/index3.html
   von Schuckmann, K., Cheng, L., Palmer, D., Hansen, J., Tassone, C., Aich, V., Adusumilli, S., Beltrami, H., Boyer, T., Cuesta-Valero, F., Desbruyeres, D., Domingues, C., Garcia-Garcia, A., Gentine, P., Gilson, J., Gorfer, M., Haimberger, L., Ishii, M., Johnson, G., Killick, R., King, B., Kirchengast. G., Kolodziejczyk, N., Lyman, J., Marzeion, B., Mayer, M., Monier, M., Monselesan, D., Purkey, S., Roemmich, D., Schweiger, A., Seneviratne, S., Shepherd, A., Slater, D., Steiner, A., Straneo, F., Timmermans, ML., Wijffels, S. (2020). Heat stored in the Earth system: where does the energy go? Earth System Science Data (Volume 12, Issue 3, 07 September 2020), 2013-2041.
7. Velicogna, I., Mohajerani, Y., A, G., Landerer, F., Mouginot, J., Noel, B., Rignot, E., Sutterly, T., van den Broeke, M., van Wessem, M., Wiese, D. (2020). Continuity of ice sheet mass loss in Greenland and Antarctica from the GRACE and GRACE Follow‐On missions . Geophysical Research Letters (Volume 47, Issue 8, 28 April 2020, e2020GL087291.
8. National Snow and Ice Data Center
   World Glacier Monitoring Service
9. National Snow and Ice Data Center
   Robinson, D. A., D. K. Hall, and T. L. Mote. 2014. MEaSUREs Northern Hemisphere Terrestrial Snow Cover Extent Daily 25km EASE-Grid 2.0, Version 1 . [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/MEASURES/CRYOSPHERE/nsidc-0530.001 . [Accessed 9/21/18].
   http://nsidc.org/cryosphere/sotc/snow_extent.html
   Rutgers University Global Snow Lab, Data History Accessed September 21, 2018.
10. R. S. Nerem, B. D. Beckley, J. T. Fasullo, B. D. Hamlington, D. Masters and G. T. Mitchum. " Climate-change–driven accelerated sea-level rise detected in the altimeter era. " PNAS , 2018 DOI: 10.1073/pnas.1717312115
11. https://nsidc.org/cryosphere/sotc/sea_ice.html
    Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS, Zhang and Rothrock, 2003)
    http://psc.apl.washington.edu/research/projects/arctic-sea-ice-volume-anomaly/
    http://psc.apl.uw.edu/research/projects/projections-of-an-ice-diminished-arctic-ocean/
12. USGCRP, 2017: Climate Science Special Report: Fourth National Climate Assessment, Volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 470 pp, doi: 10.7930/J0J964J6
13. http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F
14. http://www.pmel.noaa.gov/co2/story/Ocean+Acidification
15. C. L. Sabine et.al., “ The Oceanic Sink for Anthropogenic CO 2 ,” Science vol. 305 (16 July 2004), 367-371

Special Report on the Ocean and Cryosphere in a Changing Climate , Technical Summary, Chapter TS.5, Changing Ocean, Marine Ecosystems, and Dependent Communities, Section 5.2.2.3.
https://www.ipcc.ch/srocc/chapter/technical-summary/

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Source

1. NASA. (2020, October 6). Climate Change: How do we know? Retrieved from http://climate.nasa.gov/evidence/

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