ADDITIONAL QUESTIONS FOR THE RECORD 1. During the course of the hearing, Dr. Michaels provided a chart which purported to show that a key model used by the IPCC did not provide an adequate representation of temperature data in the 5,000-30,000 ft. layer gathered by satellites over the past 20 years. Please provide your own views on the methodology and interpretation used in this chart and its significance, if any, to the validity of the IPCC models. Answer: The chart which Dr. Michaels included in his testimony as Figure 1 compares two quite different measurements of temperature (surface observations and satellite observations of the middle troposphere). The differences between the two records provide useful scientific information and also illustrate some basic shortcomings in the logic of Dr. Michaels in expecting the records to be identical, or to be directly comparable to the model results of Manabe. There are three problems: (i) a seventeen year record cannot be used to derive a long-term trend in the Earth's temperature because the temperature fluctuates too much on such a short time scale due to a variety of natural phenomena; (ii) the observations cannot be compared to a model that does not include all natural and anthropogenic phenomena that affect temperature; and (iii) trends in surface temperature may be different from trends in mid-troposphere temperature. A seventeen year record cannot be used to derive a long-term trend in the Earth's temperature because the temperature fluctuates too much on such a short time scale due to a variety of natural phenomena: The Microwave Sounding Unit (MSU) satellite record is a measurement of the temperature of the free troposphere (generally the middle tropospheric layer from about 5,000 to 30,000 feet, but with some influence from even higher layers); Dr. Michaels curve shows the average from thousands of these measurements over the two hemispheres over about a 15 year period. It is important to recognize that the surface and satellite observational records show a response to all of the factors that have caused temperature change over this period, including not only increases in the concentrations of greenhouse gases and aerosols, but also of volcanic dust injections (particularly from the El Chichon eruption in 1983 and the Mt. Pinatubo eruption in 1991), of El Nino variations in the Pacific Ocean, of changes in stratospheric ozone concentration, and of other natural and anthropogenic influences. Like the surface record, the MSU record is quite variable and attempting to determine a long-term trend from this relatively short record is fraught with statistical uncertainties. Trend analyses can give very different results depending over what period the calculations are made and what region is selected. It is generally preferred that records be 30 years or longer and that account be taken of special events such as volcanic eruptions that may affect the record. When the mid-tropospheric temperature record is extended back to the 1960s using radiosonde observations, the longerterm trend shows a significant warming, broadly consistent with ground-based observations and roughly as expected from the newest climate model simulations that incorporate the affect of aerosols. Dr. Michaels does not seem to want to mention this support for the predicted global warming trend. Observations cannot be compared to a model that does not include all natural and anthropogenic phenomena that affect temperature: The observations cannot be compared to the model results used by Dr. Michaels because the model simulation assumed that the only factor affecting climate was increasing atmospheric concentrations of carbon dioxide (assumed to be 1% per year). No attempt was made in the model to account for the temperature influences of volcanic eruptions, changes in anthropogenic aerosols, or lower stratospheric ozone depletion during this period, all of which would be expected to have had cooling influences on the troposphere. Dr. Michaels had to adjust the model results for a number of reasons: (i) the original simulation was not for any particular year, (ii) the actual rate of increase of carbon dioxide is less than that assumed in the simulation; and (iii) other greenhouse gases were not simulated. The approach used by Dr. Michaels to adjust the model results is highly questionable. Finally, given the natural variability of the climate, Dr. Michaels should know that comparing the results for a particular observational period and a particular model simulation is not statistically appropriate. It is essential, if a comparison is to be made, for there to have been an ensemble of simulations, each including the variety of factors influencing the global temperature. Trends in surface temperature may be different from trends in mid-troposphere temperature: Dr. Michaels next contends that the surface temperature trends should be the same as the MSU trends. However, before noting a number of reasons for why these records may not be identical I would note that the trends deduced from satellite data over land are not too dissimilar from the trends deduced from land-surface observations. The lack of an observable trend in the satellite record is because there is a warming over land areas and a cooling over the oceans. I would also like to note that if the affects of El-Nino and the Mt. Pinatubo eruption are taken out of the record them even the satellite data shows a warming trend. There are a number of reasons why these records may not be directly comparable. First, recent analyses by Hurdle and by Jones and Santer confirm that, at particular locations, temperature variations at the surface and in the middle troposphere can be quite different. While tropospheric and surface temperatures are connected under many weather regimes, they become disconnected under the many weather regimes when a temperature inversion forms (e.g., on quiet winter nights when the surface temperature cools well below the temperature of the overlying air and throughout the subtropics where the descending air in the troposphere creates a near surface inversion). Analyses of the global patterns of these differences suggest that the differences are largest for just those circulation patterns when warming due to greenhouse gases is most likely. Second, differences occur because sea surface temperatures are relatively stable. Under wintertime conditions over the oceans, the mid-tropospheric temperature measured by the MSU instrument can vary strongly (e.g., in the region of the Aleutian low pressure system where Pacific storms form), while the sea surface temperatures vary only fairly slowly. Thus, whereas land surface temperatures can vary more than tropospheric temperatures, sea surface temperatures will vary only a little. Along with the finding that over land, especially in the winter and on summer evenings, the surface temperature can vary much more than the air temperature, these differences mean that surface and tropospheric temperature measurements are recording quite different quantities. Third, lower stratospheric ozone depletion is likely to have affected the mid-tropospheric temperature trends more than the surface temperate trends. The counter-arguments of Dr. Michaels on this issue are again highly questionable because the geographic region of maximum ozone depletion does not have to coincide directly with the geographic region of maximum affect on tropospheric temperatures. I are quite confused about why Dr. Michaels plots the two curves with an offset-he somehow seems not to have adjusted to a common reference level. If this is to show that there is an offset between greenhouse gas only simulations versus the new simulations including sulfate aerosols, I agree. When the cooling influence of aerosols is accounted for, the two curves come into broad agreement (recognizing the differences in the two quantities discussed earlier). To more properly investigate the accuracy of model simulations, I would invite Dr. Michaels to prepare a comparison of an ensemble of the newest model simulations with the extended record of surface temperature changes. It is such a comparison that has been relied upon by the IPCC and led to their conclusion that the agreement between model results and observations is suggestive of a “discernible human influence on the climate." I concur with this IPCC finding. 2. During the course of the hearing, Dr. Michaels provided a chart which purported to show that all of the temperature change from 1965 to 1994 occurred in one year, a feature which models cannot predict. Dr. Michaels implied that the inability of models to predict such behavior called into question their use for policy purposes. Please provide your own views on the methodology and interpretation used in this chart and its significance, if any, to the validity of climate models. Answer: Both the simple climate models and the General Circulation Models used by IPCC are suitable for policy formulation. The fact that they do not simulate every bump and wiggle in the observational record is not surprising given they do not attempt to simulate every natural phenomena that affects the Earth's climate on short time scales. First, I want to note that the record that Dr. Michaels showed was of the radiosonde record, which is a measure of the free troposphere temperature. As indicated in my answer to the previous question, this record may not be exactly the same as the surface temperature record and it has likely been affected by the cooling influence of the lower stratosphere ozone depletion suppressing warming in the last part of the record. With respect to the statistical analysis, as Dr. Michaels frequently points out, there is considerable natural variability from one year to the next, hence one needs to be very careful of creating break points at particular time periods, because this can distort the interpretation of the record. Interestingly, this is precisely what Dr. Michaels has done in his analysis of the chart in question. What is interesting is that the temperatures stayed elevated-unlike natural fluctuations, the average did not return to its pre-jump level, hinting that this is likely a human-induced warming. Given that many factors influence the Earth's temperature, and most models do not attempt to simulate all of them, temperature discontinuities should not be unexpected. Observations suggest that major changes in circulation can occur over short periods and persist for some years. Thus, the climatic regime can shift into drought or high precipitation conditions in California, the Sahel, and other regions and last for many years or more. There are suggestions that these shifts result mainly from changes in ocean circulation, which can shift rather dramatically over short periods (e.g., El Nino events in the Pacific Ocean and interruption of the thermohaline circulation in the North Atlantic Ocean). Therefore, at certain times a number of factors (e.g., onset of an ENSO event, recovery for a volcanic eruption, etc.) could all affect temperature in the same direction. These factors would be superimposed on the long-term warming trend caused by greenhouse gases. It is true that climate models that include only the atmosphere do not reproduce large interannual shifts in the climate, but the new models that include a fully dynamic ocean representation are showing rather significant shifts in the climate are possible over short periods. That the natural climate can seemingly relatively easily shift modes should not, however, make us complacent, rather, we should be very concerned that human influences on the climate might lead to shifts in the climate of the future into new modes to which society is not well adapted. 3. You testified that the IPCC assessment finds that aggregate global food production under projected climate change conditions should be able to keep pace with population growth and nutritional needs. In making this pʊjection, how does the IPCC take into account the increasing air pollution in many developing countries, soil erosion and degradation, competing demands for land and water, growing populations, the need for fertilizers, sea level rise onto productive river delta lands, and other factors that may limit the availability of agriculture to shift or increase production? What is the range of uncertainty of this projection and what are the chances that the actual consequences could be much worse? Answer: The IPCC's rather optimistic assessment that overall global food production can rise sufficiently to provide for expected population and economic growth over the next few decades is based on a combination of factors, including improved varieties and management as a result of scientific research, plus the physiological benefits to crops of CO2 enrichment. The IPCC chapter concluded that on the whole, new studies of climate change impacts on agriculture "support the evidence presented in the first IPCC assessment in 1990 that global agricultural production can be maintained relative to baseline production in the face of climate changes likely to occur over the next century (i.e., in the range of 1.0 to 4.5 C) but that regional effects will vary widely." This broad conclusion was specifically focused on the marginal effects of climate change on baseline production; that is, climate change, itself, was not judged to present a major problem for overall global production providing that those regions that become more suitable for agricultural production are able to expand production even as production in other regions contracts. Further, all areas will need to make adjustments in the varieties of crops planted, livestock raised, and the techniques and practices used in production (e.g., the timing of field operations, amount of irrigation, tillage practices). However, the key issue may not be global food production, but regional food production. Areas where climate change reduces food production potential may face production declines even if all economically practical adaptations are made. As the IPCC emphasizes, poorer populations in regions negatively affected by climate change are most vulnerable to the more serious consequences of hunger and famine. Thus, there will be losers as well as winners in the process of climate change. The likely winners will be some of the industrialized countries of the northern hemisphere's cool temperate zones (including such countries as Canada and Russia). The likely losers, on the other hand, will be countries in the tropics and subtropics, particularly those with semiarid and arid regions located inland. In such areas, increasing frequency, duration, and severity of drought as well as of heat spells may cause instability and crop failures. The areas in question include not only most of Africa and parts of Asia and South America, but also the Southern Great Plains of the USA. The regional effects could be very strong even in the United States, with some current farming areas becoming unproductive without major new investments in irrigation (and assuming water supplies are available). Hence, America may lose its capacity to produce large grain surpluses, and to offer them to the hungry nations. This is particularly important because the economic gap between the developed (industrialized) countries, and the developing nations (especially in Africa) is likely to widen. The developing nations may well suffer more episodes of famine, thereby generating greatly increased numbers of environmental refugees. As a consequence, the developing nations will become increasing dependent on the largess of the rich nations just when their production may be somewhat limited due to climate change. An important limitation of the IPCC effort was that it was not able to independently assess the many environment, resource, and technology factors that may lead to either increases or greater constraints on production in the future. However, climate changes will certainly exacerbate worrisome trends of denudation and land degradation (including erosion) in most semiarid and arid regions, where population growth exerts increasing pressure on fragile and limited soil and water resources. Sea-level rise will threaten the productivity of low-lying coastal zones such as the Nile Delta of Egypt, Bangladesh, island nations, and even parts of the US (Florida and the Mississippi Delta). The IPCC also noted that the baseline agricultural production for their estimates (what agricultural production will be in the future if climate change did not occur) is widely debated. The IPCC reviewed the studies of agricultural experts from the World Bank, the UN Food and Agriculture Organization, and the International Food Policy Research Institute that project world food production into the future. Each of these projections show, in the absence of climate change, increasing world food availability in the future with production expanding faster than population and world commodity prices falling. A limitation of these studies is that they only extend to the year 2010 or 2020. Other studies are less optimistic, citing limits on further land expansion and irrigation, resource degradation, and reduced confidence that the historical rates of increase in yield will continue. Factors that will determine whether agricultural supply can keep pace with demand include: (1) how fast demand grows in response to population and economic factors, (2) the future availability and quality of land, (3) the future availability of water, and (4) whether improvements in technology will continue to result in rapid yield growth. Further, economic growth and development are closely tied to demand growth and, in many developing countries, are also dependent on agricultural development. Considering each of these issues separately. •Demand growth. Between 1950 and 1990, world population grew at a 2.25% compound annual rate. Through 2025, population is projected to grow at a compound annual rate of between 1.13% and 1.55% (high and low UÑ variants). The decade of the 1990s is projected to have the largest absolute population addition, with declining additions in subsequent decades. Thus, growth in food supply could slow by 40 to 50 percent from recent decades while maintaining per capita food production levels. Income growth will likely cause demand to grow more rapidly than population and will change the composition of demand, most likely away from food grains and toward meat, fruits, and vegetables. The shift to meat is likely to increase the demand for grain for livestock feed. Increased demand generated by increased income growth would allow more and higher quality food to be consumed per capita but this depends on how food consumption is distributed. Beyond 2025, population growth is generally projected to be reduced because world population is projected to stabilize by around 2075, but this is an assumption that may be optimistic. • Land quantity and quality. Some estimates suggest that there is much potentially-available land, but the cost of bringing it under production may be high with attendant adverse environmental impacts limiting expansion. Intensification of production on existing cropland may worsen land degradation and put additional pressure on water and soil resources. Firm data on the extent and severity of land degradation and its impact on production potential for most of the world are not available, but the recent overview, although still qualitative in economic terms, confirms significant degradation and loss of arable land, especially in Africa. Studies disagree on the extent to which intensification of use affects land degradation. Competition for agricultural resources for other uses may also affect the supply and price of land for agriculture. Carbon sequestration, biomass energy production, forest product production, the potential development of new non-food agricultural products, and removal of agricultural land from production for other environmental objectives will all likely affect the amount of land available for food production. • Water supply and irrigation. Irrigation has contributed significantly to increased production in the past. Currently, 17% (253 million hectares) of global cropland is irrigated, but this 17% of land accounts for more than one-third of total world food production. An estimated additional 137 million hectares have the potential to be irrigated, but the cost of doing so may be prohibitive. Current water systems in many developing countries achieve low efficiencies of water distribution, and average crop yields are well below potential. There are environmental and health-related effects of irrigation such as soil salinization and the spread of water-borne diseases that may limit further expansion. Major factors contributing to these irrigation problems in both developing and developed countries are: un-priced and heavily subsidized water resources; inadequate planning, construction and maintenance of water systems; unassigned water rights or rules that limit the transfer of rights; and conflicts between development and distribution goals. Solutions to these problems are available in most cases and a recent study found that investments in irrigation have been at least as profitable as investments in other agricultural enterprises. Changes in potenti:!.rrigation water supply due to climate change have not, with few exceptions, generally been integrated into agricultural impact studies. •Future yield growth. Assumed continuation of yield increases due to improving technology and further adoption of existing technologies is uncertain. Gaps between actual and potential |