हिस्सा 15: What should we expect? Future climate projections

The last house on Holland Island, मैरीलैंड, where 360 people lived before tides took over. Photograph by Astrid Riecken for the Washington Post/Getty Images retrieved from National Geographic Daily News.

By Luisa Cristini, PhD, University of Hawaii at Manoa

Note from the editor: This is the fifteenth and last in a series of blog entries that focused on introductory topics in climate dynamics and modeling, और विज्ञान की वर्तमान समझ में अंतर्दृष्टि प्रदान करने के लिए कार्य किया.]

जलवायु परिवर्तन के बढ़ते सबूत को देखते हुए, what should we expect our future climate to be like? A large number of simulations are available from a broad range of climate models. Together with additional information from observations, they provide a quantitative basis for estimating likelihoods for many aspects of future climate change. Model simulations run for the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (आईपीसीसी) में 2007 cover a range of possible futures based on possible greenhouse gases emissions. The IPCC assessment relies on a large number of climate models of increasing complexity and realism, as well as information on the feedbacks from the carbon cycle and climate observations.

Surface air temperature: Numerical model experiments show that even if carbon dioxide emissions were held constant at year 2000 स्तर, a global surface air temperature increase would occur in the next two decades at a rate of about 0.1°C per decade, due mainly to the slow response of the oceans. About twice as much warming is expected when emissions are within the range of the SRES scenarios (discussed in हिस्सा 14). Best-estimate projections from models indicate that decadal average warming over each continent by 2030 is independent of the scenario chosen and is very likely (probability of occurrence higher than 90%) 20 वीं सदी के दौरान इसी मॉडल से अनुमान लगाया प्राकृतिक परिवर्तनशीलता के रूप में कम से कम दो बार के रूप में बड़े होने के लिए. Continued greenhouse gas emissions at or above current rates will cause further warming and induce changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century. इसके अलावा, increase in temperature tends to reduce land and ocean uptake of atmospheric carbon dioxide, आगे वातावरण में रहता है कि anthropogenic उत्सर्जन का अंश बढ़ाने. The projected warming in the 21st century shows scenario-independent geographical patterns as observed over the past decades. Warming is expected to be greatest over land and at most high northern latitudes, and least over the Southern Ocean and parts of the North Atlantic Ocean.

Precipitation: Increases in the amount of precipitation are very likely in high latitudes (toward Earth’s poles) घटने सबसे उपोष्णकटिबंधीय भूमि क्षेत्रों में होने की संभावना है, जबकि (भूमध्य रेखा के करीब).

चरम सीमाओं: यह बहुत संभावना है कि गर्म चरम सीमाओं, heat waves and heavy precipitation events will continue to become more frequent.

Tropical cyclones: It is likely (probability of occurrence higher than 66%) that future tropical cyclones (typhoons and hurricanes) will become more intense, with larger peak wind speeds and heavier precipitation associated with ongoing increases of tropical sea surface temperatures. There is less confidence in projections of a global decrease in numbers of tropical cyclones. Extra-tropical storm tracks are projected to move poleward, with consequent changes in wind, precipitation and temperature patterns.

समुद्र का स्तर बढ़ने: 21 वीं सदी के अंत में वैश्विक समुद्र का स्तर बढ़ने के मॉडल के आधार पर अनुमान (excluding future rapid dynamical changes in ice flow from the Greenland and Antarctic ice sheets), range between 0.18 और 0.59 m, relatively to the average sea level between 1980-1999. The ocean’s thermal expansion is projected to be a major contributor to this rise.

Ocean acidification: Increasing atmospheric carbon dioxide concentrations lead to increasing ocean acidification, as explained in the article “Ocean acidification and the ’short-term‘ marine carbon cycle” by German marine geologist and PhD candidate Franziska Kersten. SRES परिदृश्यों पर आधारित अनुमानों के औसत वैश्विक सतह सागर पीएच में कटौती दे (वृद्धि की अम्लता को इसी) of between 0.14 और 0.35 units over the 21st century, adding to the present decrease of 0.1 units since pre-industrial times.

Sea ice: Sea ice (the ice formed on the ocean surface when the water freezes) is projected to shrink in both the Arctic and Antarctic. कुछ अनुमानों में, आर्कटिक देर से गर्मियों में समुद्री बर्फ के लिए 21 वीं सदी के उत्तरार्द्ध से लगभग पूरी तरह से गायब हो जाता है.

Meridional Overturning Circulation (MOC): It is very likely that the MOC, a system of surface and deep ocean currents, of the Atlantic Ocean will slow down. The multi-model average reduction by 2100 है 25%. This could mean a decrease in warm water reaching the eastern coasts of the North Atlantic Ocean (जी, Europe). तथापि, temperatures in the Atlantic region are projected to increase despite such changes due to the much larger warming associated with projected increases in greenhouse gases. It is very unlikely (probability of occurrence less than 10%) that the MOC will undergo a large abrupt transition during the 21st century.

Climate-carbon cycle coupling is expected to add carbon dioxide to the atmosphere as the climate system warms, but the magnitude of this feedback is uncertain. Based on current understanding, model studies suggest that to stabilize carbon dioxide concentration at 450 ppm (मिलियन प्रति भागों) could require that cumulative emissions over the 21st century be reduced from an average of approximately 670 GtC (gigatons of carbon, मैं, कार्बन के अरबों टन) लगभग करने के लिए 490 GtC.

ग्रीनलैंड बर्फ की चादर: Contraction of the Greenland Ice Sheet is projected to continue to contribute to sea level rise after 2100. Ice-sheet models suggest that mass losses increase with temperature more rapidly than gains due to precipitation and the surface mass balance becomes negative (meaning that the ice sheet loses mass) at a global average warming in excess of 1.9°C to 4.6°C relative to pre-industrial values. A negative surface mass balance sustained for millennia would lead to virtually complete elimination of the Greenland Ice Sheet and a resulting contribution to sea level rise of about 7 m.

Antarctic Ice Sheet: वर्तमान मॉडल के अध्ययन अंटार्कटिक आइस शीट व्यापक सतह पिघलने के लिए भी ठंडा रहेगा और वृद्धि की वजह से बर्फबारी के जन में लाभ की उम्मीद कर रहा है कि परियोजना. तथापि, बर्फ मुक्ति बर्फ की चादर जन संतुलन हावी अगर बर्फ द्रव्यमान का शुद्ध घाटा हो सकता है.

दोनों अतीत और भविष्य मानवीय कार्बन डाइऑक्साइड के उत्सर्जन एक सहस्राब्दी से अधिक के लिए वार्मिंग और समुद्र का स्तर बढ़ने के लिए योगदान करने के लिए जारी रहेगा, due to the time scales required for removal of this gas from the atmosphere and the slow response of major climate components such as oceans and ice sheets.


References and further resources

Goosse H., P.Y. Barriat, में. Lefebvre, M.F. Loutre and V. Zunz (2012). Introduction to climate dynamics and climate modeling. Online textbook available at http://www.climate.be/textbook/chapter6_node2.htm

आईपीसीसी (2007): Summary for Policymakers. में: जलवायु परिवर्तन 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, एस, डी. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, कैंब्रिज, United Kingdom and New York, NY, अमेरिका. http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-spm.pdf