A major component of climate models is the inclusion of radiative-forcing agents, which enables the models to then simulate future climates. Therefore, climate models need information on how emissions and concentrations of things such as greenhouse gases aerosols will change in the future. Check out the table below showing the dozens of climate models and the forcing agents used in them.
Q1: In addition to ozone, what four other greenhouse gases or groups of greenhouse gases are included in nearly all the climate models?
Climate models can't model future climate without projections of future emissions of greenhouse gases and aerosols. Therefore, scientists and policy makers have created several different emissions scenarios for use in the IPCC's Fifth Assessment Report. Watch the video below showing Dr. Sara Harris of the University of British Columbia (UBC) explain future emissions scenarios. This video is from Module 6.1 of UBC's course Climate Literacy: Navigating Climate Change Conversations.
Q2: With respect to the representative concentration pathways, what is the largest of the four hypothesized radiative forcings from pre-industrial times to 2100? The anthropogenic radiative forcing from 1750-2011 was 2.3 W m-2.
The three figures below expand on what you just saw in the video, which only showed projected CO2 emissions. The figures show projected CO2, CH4, and N2O emissions over the rest of the century. The scenario referred to as RCP3PD is named RCP2.6 hereafter in the lab.
Q3: What two emissions scenarios most closely represent the current trend in CO2 emissions?
Below are the projected CO2, CH4, and N2O concentrations over the rest of the century. The atmospheric lifetimes of CO2 and N2O are approximately 100 years, while the lifetime of CH4 is roughly a decade. Near-term climate change is for the period 2016-2035, while long-term climate change is 2081-2100.
Q4: Why are CO2 concentrations increasing under the RCP4.5 scenario when emissions are decreasing?
Section 3: Projected Temperature Changes
Combining the results from many climate models shows provides information like that provided in the figure below; it shows projected changes in the mean global temperature from 2005 to 2100. The values are differences from the mean global temperature from 1986-2005; therefore, the values are anomalies. The black line is an extrapolation of the linear trend in observed global temperature from 1979-2015.
Q5: If we assume the current trend in temperatures will continually to occur until 2035, then how would you describe the projected changes from the four different scenarios in the near term (i.e., 2016-2035)?
Q6: Which scenario produces projections in the long term (i.e., 2081-2100) that most closely resembles the current trend in temperatures?
As you have seen the RCP6.0 and RCP8.5 scenarios matches an extrapolation of the current trend in CO2 emissions, while the RCP4.5 scenario in the long term most closely matches an extrapolation of the current trend in the mean global temperature. You also may have noticed that there was little disagreement among the scenarios with respect to projected emissions, concentrations, and temperatures in the near term. The RCP4.5 scenario is a "middle-ground" scenario, and the figures below show spatial variations in projected near-term temperatures under the RCP4.5 scenario. December-February and June-August are winter and summer, respectively, in the Northern Hemisphere.
Q7: Why isn't the Arctic region projected to warm more in the summer than in the winter? Think of a process that is consuming energy and not allowing that energy to become sensible heat.
Q8: If the figure above reflected results from using the RCP8.5 scenario in the climate models, then how would the temperature changes in the Arctic region differ from what you observed in the figure?
Section 4: Projected Changes in Evaporation and Atmospheric Moisture
The climate models also project changes in sea-surface temperature (SST), evaporation, and specific humidity, along with many other variables. The figures below show projected changes in SST, evaporation, and surface specific humidity in the near-term under the RCP4.5 scenario.
Q9: What is the connection between SST and specific humidity? Think about the hydrologic cycle.
Q10: How might the projected increase in specific humidity affect the intensity of storm systems?
As you saw in the figure of projected mean global temperatures, there is a much larger temperature spread among the scenarios in the long term than in the near term. The figures below show projected changes in temperature from 1986-2005 to 2081-2100 under the four different scenarios.
Q11: Why are land masses projected to warm more than the nearby oceans?
Q12: What is the maximum amount of projected warming for any part of the Arctic? What is this warming in °F?
Section 5: Projected Changes in Storms, Precipitation, and Soil Moisture
Climate models also can make rough predictions in changes in the general locations of extratropical storms (i.e., storm systems poleward of the tropics). The figure below shows how the location of storm tracks in the winter season might change by the end of the century. Results using the RCP4.5 and RCP8.5 scenarios are shown for the Northern Hemisphere in the top two panels and for the Southern Hemisphere in the bottom two panels. The top two panels show the Northern Hemisphere and the bottom two panels show the Southern Hemisphere. It may seem somewhat counter-intuitive that places with projected decreases in extratropical storms are shown in shades of blue.
Q13: How are the paths of extratropical storms expected to change?
Q14: What extratropical regions not in Asia should experience much less rainfall in the future based on the projected changes in storm tracks?
As you hopefully recall from Lab 3 (The Troposphere), a major feature of the tropics and subtropics is the Hadley Cell. This is the large-scale movement of air in the troposphere, with rising air at the ITCZ and sinking air outside the tropics in areas known as subtropical high-pressure cells. Humid air rises at the ITCZ, typically forms deep cumulonimbus clouds as it goes to the top of the troposphere, and then the air heads poleward and sinks in subtropical areas (i.e., subtropical highs). The figure on the right below shows projected changes by the end of the century in the locations of the northern and southern edges of the Hadley Cell under the RCP4.5 scenario.
Q15: How is the width of the Hadley Cell expected to change?
Q16: What regions should experience much less rainfall in the future based on the projected changes in the Hadley Cell?
Precipitation is an extremely difficult variable for climate models to predict, as illustrated by the hatching (i.e., low confidence in projections) in the figures below. The figure on the left shows projected precipitation changes in the near term under the RCP4.5 scenario. The figure on the right shows projected precipitation changes in the long term under the RCP8.5 scenario.
Q17: How is Arctic precipitation projected to change?
Q18: Why is precipitation over the Mediterranean region expected to decrease?
Climate models also can project future soil-moisture conditions. The amount of soil moisture is controlled by soil type, precipitation, and temperature. The figures from left to right show (1) projected near-term changes in soil moisture under the RCP4.5 scenario, (2) projected long-term changes in soil moisture under the RCP4.5 scenario, and (3) projected long-term changes in soil moisture under the four different scenarios.
Q19: What specific changes in two climate variables are expected to lead to major decreases in soil moisture southern Africa and the Mediterranean region?
Q20: How might agriculture in southern Europe change by the end of the century if conditions follow the RCP8.5 scenario?
The figure below summarizes the information in this section and the previous section by showing the general changes to the hydrologic cycle by the end of the century.
Q21: How do the subtropics differ from high latitude areas with respect to changes in the hydrologic cycle?
Section 6: Projected Changes to the Cryosphere
The graphic below shows observed changes to the cryosphere, and you examined this graphic at the end of the previous lab.
Q22: Which of the changes noted in the figure above do you expect to continue throughout the rest of the century?
Sea ice in the Northern Hemisphere reaches a maximum extent in February and a minimum extent in September. The image below shows projected changes in Northern Hemisphere sea ice over the rest of the century.
Q23: Under the RCP4.5 scenario, how much is sea-ice extent in February expected to decrease from the 1986-2005 value by 2100? How much of a decrease is this in percent (i.e., divide the change by the 1986-2005 sea-ice extent value)?
Q24: Under the RCP4.5 scenario, how much is sea-ice extent in September expected to decrease from the 1986-2005 value by 2100? How much of a decrease is this in percent (i.e., divide the change by the 1986-2005 sea-ice extent value)?
The image below shows where sea ice in the Northern Hemisphere is expected to decrease. Please be aware that not only is sea ice projected to decrease in extent but is also is projected to decrease in thickness, thereby continuing the current trends.
Notice that at the end of the century the Arctic Ocean is projected to be completely ice-free in late summer under the RCP8.5 scenario.
The extent and thickness of permafrost has been decreasing over the past several decades, and these changes are projected to continue. The figure below shows how the extent of permafrost, in millions of square kilometers, is projected to change by the end of the century under the four RCP scenarios.
Q25: Based on the projected changes in permafrost area in the above figure, what climate type and what biome do you expect to shrink substantially in size by the end of the century?
Section 7: Projected Changes in Sea Level
Towards the end of the previous lab you learned that the observed rise in global mean sea level from 1993-2010 was 3.2 mm yr-1,and that thermal expansion was the largest contributor to the sea-level rise. If this rate of sea-level rise were to continue for 100 years the global mean sea level would rise by 0.32 meters.
Q26: What do you think is going to be the major contributor to sea level rise at the end of the century
Q27: What will continue to be the two major causes of sea level rise?
The figure below shows the projected changes in sea level under the RCP4.5 scenario. And obviously coastal areas are the most impacted by sea-level changes. The Marshall Islands are one example of a region being impacted by past sea-level rise.
Q28: How is rising sea level affecting the Marshall Islands?
Q29: Based on the predictions in the above graphic, what is the prognosis for the Marshall Islands and other low-lying islands and coastal areas by the end of the century?
Section 8: Projected Changes to Biomes
Biomes, which are formations of flora and fauna that have common characteristics, are controlled by the climate of a region. Throughout this lab you have seen that there might be dramatic changes in climate across the globe by the end of the century; therefore, there could be major shifts to biomes. You can observe possible changes in climate types from the present time to the end of the century be viewing the following Google Earth files: 1976-2000 and 2076-2100. These data were provided by the Institute of Veterinary Public Health of Vetmeduni Vienna.
Q30: What is the general movement of climate types (and thus biomes) in the middle and high latitudes of the Northern Hemisphere as you switch from 1976-2000 to 2076-2100?
Q31: What biome would you expect to decrease the most in extent by the end of the century?
The figure below shows observed and projected changes associating with warming-induced shifting of the boreal forest and tundra biomes. Warming has caused the biomes to shift northwards, and the projected wrming is expected to continue the northward shift.
Q32: What process resulting from the melting of tundra would lead to increased global warming?
Write responses of one to two sentences for each of the following big questions of the lab.
Q33: By the end of the century, how are temperatures across the globe projected to change under the scenarios with increasing CO2 concentrations
Q34: How will continued increases in global temperature affect the global hydrologic cycle?
Q35: If global warming persists, how will the distribution of biomes at the end of the century differ from the current distribution?
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