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Causes of Climate Change What Is the Greenhouse Effect?

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Causes of Climate Change What Is the Greenhouse Effect? CLIMATE CHANGE page 4 Q1: Is climate changing? Q2: Hasn’t climate always changed? Q3: Is the recent warming a recovery from the “Little Ice Age?” Q4: Hasn’t the “hockey stick” graph showing warming been proven wrong? table of Q5: I heard that some of Antarctica was cooling. Does this mean that global warming is wrong? Q6: Are variations in solar energy causing climate change? CONTENTS CAUSES OF CLIMATE CHANGE page 12 Q7: What is the greenhouse effect? Q8: Since CO2 increases lag behind temperature rises, as shown in ice cores, how does C02 relate to climate change? Q9: How do we know recent C02 increases are due to human activities? Q10: How do we know that recent climate change is caused by humans? ICE SHEETS, SEA LEVEL AND IMPACTS OF CLIMATE CHANGE page 18 Q11: Aren’t climate predictions based on untested computer models? Q12: How can we trust long-term predictions if we can’t forecast next week’s weather? Q13: What is so bad about a little warming? Q14: Can anything be done about climate change? Q15: How will climate change affect me? Q16: Why should I be worried about sea-level rise? Q17: Haven’t the ice sheets survived warming in the past? Q18: Won’t melting of the ice sheets take a long time? Q19: Are there tipping points for ice sheets? Q20: Why all the excitement about the Antarctic and Greenland ice sheets, when they are changing only a little bit? Photo by Kees van der Veen, Greenland, 2003 section one CLIMATE CHANGE Photo by Kees van der Veen, Greenland, 2004 Q1 Q2 IS CLIMATE CHANGING? HASN’T CLIMATE ALWAYS CHANGED? YES. There is a consensus continues to build and prestigious indicated by worldwide retreat of YES. Natural changes have factors such as variations in the relatively stable climate. Changes among scientists that climate scientific organizations endorse mountain glaciers and snow cover, occurred in the past, with earth’s orbit and volcanic expected from continuing human change is occurring, with the list these conclusions. Temperature decreased sea-ice cover in the variations in temperature and activity. Rapid climate shifts have activity will be global, much more of skeptics slowly shrinking. records, including those far from Arctic during the summer, CO2 concentrations documented occurred occasionally in the past, rapid than similar large changes This consensus has been strength- cities and over the oceans, are melting permafrost, and shifts in from ice cores, tree rings, and although scientists continue to de- that occurred in the past, and will ening over time as evidence of not the only evidence used by biological activity with animals and many other climate archives. bate whether these were regional or have greater impact because of increasing global temperatures scientists. Warming is also plants moving polewards. These changes, however, mostly global. However, the rise of human the much larger world population. took place over tens of thousands of civilization over the last 10,000 years and were caused by natural years happened during a time of Global and hemispheric annual combined land-surface air temperature and SST anomalies (°C) (red) for 1850 to 2006 relative to the 1961 to 1990 mean, along with 5 to 95% error bar ranges, from HadCRUT3 (adapted from Brohan et al., 2006). The smooth blue curves show decadal varia- Photo by Joel Plummer, Antarctica, 2006 tion. Source: IPCC AR4 WGI 4 CLIMATE CHANGE CLIMATE CHANGE 5 Q3 IS THE RECENT WARMING A HASN’T THE “HOCKEY STICK” GRAPH Q4 RECOVERY FROM THE “LITTLE ICE AGE?” SHOWING WARMING IN THE NORTHERN HEMISPHERE BEEN PROVEN WRONG? NO. The “Little Ice Age” was increased volcanic activity, and in solar activity. Those natural NO. Evidence for the recent the Northern Hemisphere is estimate the uncertainties caused not a continuous, well-defined, changes in atmospheric circulation. causes cannot explain the mag- warming is based on direct commonly known as the “hockey by not having climate records from planetary-wide cold period but The natural warming that followed nitude and pattern of recent measurements using modern stick” graph with the 20th cen- everywhere. Although these instead consisted of several intervals the “Little Ice Age” was in response warming, especially the acceleration instruments. To estimate tem- tury warming representing the techniques continue to be improved, of below average temperatures to a decrease in the sun-blocking observed over the last few decades. peratures over the last 1000 years, upward pointing “blade”. Because resulting in minor changes in the in the Northern Hemisphere due effect of large volcanic eruptions Michael Mann and colleagues available climate records are not “hockey stick” graph, the National to decreased solar radiation, and the coincidal slight increase analyzed many climate records, evenly distributed over the planet, Academy of Sciences provided an including tree rings, thermometers, Mann and his colleagues developed extensive report confirming the and other climate archives. Their techniques to estimate tempera- general findings of Mann’s study. graph of average temperature in tures across large areas as well as Comparison between global mean surface temperature anomalies (°C) from observations (black) and model simulations. The plot above shows results from 58 simulations using 14 different models using both anthropogenic and natural forcings. The multi-model ensemble mean is shown as a thick red curve and individual simulations are shown as thin yellow curves. Vertical grey lines indicate the timing of major volcanic events. On average, these simulations do a good job at reproducing global temperatures. Source: IPCC AR4 WGI Simulated global mean temperature anomalies from 19 simulations produced by five models with natural forcings only. The multi-model ensemble mean is shown as a thick blue curve and individual simulations are shown as thin blue curves. These results, which ignore the addition of man-made greenhouse gases, do not reproduce the measured temperature changes, especially from the latter part of the 20th century until the present. Source: IPCC AR4 WGI 6 CLIMATE CHANGE CLIMATE CHANGE 7 Q5 I HEARD THAT SOME OF ANTARCTICA WAS ARE VARIATIONS IN SOLAR ENERGY Q6 COOLING. DOES THIS MEAN THAT GLOBAL CAUSING CLIMATE CHANGE? WARMING IS WRONG? NO. To determine the such as winds and ocean cur- Only two of these stations are in YES. The amount of solar the Earth’s orbit have been linked part in amplifying temperature validity and magnitude of cli- rents will influence the amount the interior of Antarctica, with energy we receive depends on to glacial cycles. Research has changes. Recent measurements mate change, we must look at of temperature rise observed at a all others located on the coast. sunspot activity and changes in shown, however, that the changes show small decreases in solar output the temperature of the en- particular location. Also, keep in Extrapolating these measurements the Earth’s orbit around the sun. in climate which occurred during over the last thirty years while at tire planet, not temperatures in mind that Antarctica is the size over the entire continent to detect Although there was a strong cor- these periods were not entirely the same time global temperatures any single location. In fact, the of the North American continent temperature trends is difficult and relation between solar energy and due to these solar deviations. continued to rise, thus empha- expected warming will likely not and has fewer than twenty stations large uncertainties remain. temperatures in the past, observations Other factors such as growth and sizing the importance that CO2 be evenly distributed across the where temperatures have been over the past few decades show recession of ice sheets and the and other greenhouse gases have planet—local weather patterns measured for several decades. that this correlation is no longer amount of CO2 transferred between in the current warming trend. dominant. For example, changes in the oceans, biosphere, and atmo- solar radiation caused by variations in sphere likely played a much larger Annual and seasonal temperature trends around Antarctica for 1951-2006. Only stations with at least 35 years of data have been used. Temperatures around the Antarctic Peninsula have warmed significantly. Stations in the interior have shown little or no change. The remaining stations around the coast of Antarctica show some warming and some cooling. Photo by Kees van der Veen, Greenland, 2003 Source: SCAR READER project. 8 CLIMATE CHANGE CLIMATE CHANGE 9 section two CAUSES OF CLIMATE CHANGE Photo by Kees van der Veen, Greenland, 2003 Q7 SINCE CO2 INCREASES LAG BEHIND Q8 WHAT IS THE GREENHOUSE EFFECT? TEMPERATURE RISES, AS SHOWN IN ICE CORES, HOW DOES CO2 RELATE TO CLIMATE CHANGE? Created through the presence of heat in the atmosphere is then from burning fossil fuels and other Through the study of air predicted well before the causing further melting of the ice certain atmospheric greenhouse partially reradiated back to the human activities. These higher trapped in Antarctic ice cores, Antarctic data showed this lag. sheets and so forth. Scientists gases, the greenhouse effect is Earth’s surface, allowing the emission rates are amplifying the scientists have determined that Glacial cycles are caused by changes have not unraveled all of the actually extremely vital to life on planet’s average surface tem- impact of the greenhouse effect, increases in CO2 happen after in incoming solar radiation, but details of what precisely caused o o our planet. This important effect perature to be about 31 C (87 F) which, in simple terms, means we increases in temperature. Some this change is not big enough changes in atmospheric CO2 over occurs because atmospheric gases warmer than it would be otherwise. are warming the planet by trapping climate skeptics have pointed to to explain the large temperature glacial cycles, but for the discussion such as CO2 and methane trap ter- Recent concerns revolve around more of Earth’s radiation, thus this fact as proof that rising CO2 swings that occur over glacial on modern climate change this is restrial radiation emitted from the the enhancement of the natural increasing the supply of energy levels are not causing the cycles.
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