Introduction to Climate Change
Climate is an essential resource for life on Earth. Quite often we take it for granted as something that has always been and something that will always be; yet, we are in an epoch when many people believe that humans are routinely affecting climate to an extent vastly beyond anything previously demonstrated. The popular press gives us a daily, sensational account of disaster reports. Much is misunderstood. Even those scientists with no vested interest in the outcome are often publicly dismissed as four-flushers. The scientific community, as a result, needs to understand and communicate the potential scale and impact of these daily experiences with not only the public but also policy decision-makers. In this book, we present some of our experiences with future climate change with the hope that those who read it will become increasingly more aware. Although this is not an entirely comprehensive book, our trust is that it provides some idea of how we approach the question of the future state of climate.
Evidence is accumulating rapidly that human activity is starting to affect the world’s climate. Nowhere is future climate change more evident than in changes presently being noted in the climate of the Arctic. Tundra vegetation, for example, is moving northwards in response to warmer temperatures in the northern tundra regions. Alaskan Inuit elders have noted significant changes in the Arctic environment over the past few years. According to the elders, rivers no longer freeze to the depth and thickness of previous years, and some villagers who live inland can no longer make their trip to the Arctic Ocean to hunt for seals. These villagers rely on the ice for transportation. Villagers were cut off last winter for three weeks because of the thinness of the ice in Cambridge Bay. Scientists also report that the number of days with ice on the Alaskan north Pacific shore has decreased from 200 to 160 per year in the last 100 years. In this area, during the winter of 1990, there was less ice in the Bering Sea than at any time since satellite records began.
Definition and Causes of Climate Change
The changes in the Earth’s climate result from various causes – many of natural origin – and are the causes of natural weather “fluctuations” or expected change upon reunification of global temperature leads. However, studies testing to understand the more complex issues of the present of current climate are or turn in the future, e.g., whether anthropogenic release of carbon dioxide will warm the Earth even further could have substantial bearing on future social and economic policies and planning. The following then, describe some basic concepts of concern to everyone, in the understanding of climate and climate change.
More than twenty years and a mountain of climatic research literature back to 1850 concern the rigorous demonstration that man-made constituents, particularly greenhouse gases, have effect on climate. Since 1955 particularly, after raises its temperature of the Earth, beginning some 60 years before 1850 in which man-made gases were generated at a significant compound in the development of industrial economies, but accumulated mainly during the past 100 years.
Climate Models and Projections
The process of forecasting the future climate is based on climate science. It involves the use of climate models, their validation, and their interpretation. Uncertainties in the model projections arise from model uncertainties and scenario uncertainties. This chapter examines these sources of uncertainty and presents the results of the ensemble modeling undertaken for the IPCC Fourth Assessment Report. New techniques for presenting both the central estimate and the range of uncertainty in the climate modeling results are introduced, with a special focus on those results that are of greatest interest to adaptation and mitigation planning.
Since the mid-19th century, the observed standard temperature record points to an increase in the global average temperature, with the changes in the last three decades being dominated by human influences. In 2007, the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) concluded, with a greater than 90% likelihood, that the observed changes in temperature are due in large part to human activities. If these changes continue and are not offset by any large cooling effects in the climate system associated with other forcings, then global climate will continue to warm throughout the 21st century. Future temperatures will depend quite strongly on the greenhouse gas (GHG) emission pathways, on the concentrations of other natural and anthropogenic forcings (chemical pollutants and particles, solar forcing, volcanic activity), and on internal climate variability.
Types of Climate Models
At the most basic level, climate models are large-scale computer programs that represent the generalized relationships between the most important processes that determine the climate system. Although historically there have been a number of different strategies taken in the construction of climate models, a simple distinction can be made between models with spectral formulations and those using grid point formulations. In spectral models, the solutions to equations that describe the large-scale motion and temperature fields are represented as a combination of spatially varying functions of some spatial scale (often sines and cosines representing a given wave number). In grid point models, the solutions are computed on grid boxes, squares of a given latitude-longitude size. At the present time, grid point models, or general circulation models (GCMs), are most commonly used to make projections of future climate change, although models with spectral approaches (including radial coordinates, or regional models) are also widely used.
GCMs have continued to increase their sophistication over the years. Early versions of these models included only the most primitive representations of certain elements of the earth’s system, such as the very small number of wave numbers used in the spectral technique for representation of the atmosphere. These models, because of this very low spectral resolution, were used mainly as tools for understanding the behavior of the most important climate processes and their variability. More recently, as computational resources have become more widely available, the climatic models have much higher resolution, includes a great deal of additional detail in the composition of the model atmosphere and ocean, and cube-sphere grids that are used to improve the distribution of land and sea area on the constructed grids and to reduce two-dimensional grid design constraints in spectral climate models. At the same time that the details of the models have increased, so too has the complexity of the physical processes they represent increased. Formerly, the basic physical parameterizations of radiation, clouds, and convection were straightforward. In current versions of the models, these basic elements have been greatly improved in sophistication (and are compounded by such processes as simple representations of land use and land cover change, with increasingly sophisticated, more realistic treatment of the physical properties).
Limitations and Uncertainties in Climate Projections
In projecting future climates, there are two types of uncertainties. The first type is the predictability of the climates with given future emissions of atmospheric constituents such as greenhouse gases and aerosols. This type of predictability is due to the complexity and nonlinearity of the climate system, with the most important impact being the level of future emissions of atmospheric constituents that will determine future trends in climate. The second type of predictability results from the climate models used to project the future climates. They pose uncertainties that cannot be ignored, even when the emissions of greenhouse gases are given. These uncertainties result from the simplifications of natural mechanisms and their poor understanding, uncertainties in the initial and boundary conditions for the models, as well as the lack of observations for the comprehensive evaluation and the construction of the models.
The limitations and uncertainties are also related to the depth of understanding about how droughts are generated or responded to the climate changes. In this respect, many possible trends in droughts are mostly derived from one available index of drought characterizing the present status of the hydrological, or soil moisture, or both conditions. Large-scale droughts may need to be projected with a Dynamic Downscaling technique to take into account uncertainties from General Circulation Models (GCMs) and also the interactions of the climate models with the land surface conditions. Climate projections provide the first-level information that is needed in assessing future opportunities and needs towards sustainable anthropogenic adaptation to long-term external changes, as long, long procedures are generally required to create new water infrastructures.
Key Climate Change Indicators
Anthropogenic warming from increased inventories of atmospheric greenhouse gases is expected to produce widespread climate impacts. The IPCC Fourth Assessment Report identified some of the observed changes in recent decades in different regions of the world, highlighting the evidence that warming is underway. Changes in climate, including changes in extremes, are also anticipated in climate models. This anticipated change includes global-mean and regional-mean temperature, precipitation and sea-level rise, and increase in hot extremes, increases in intense tropical cyclones, and shifts in temperature and precipitation associated with the El Niño-Southern Oscillation.
The basic indicators of climate change by components, prepared as part of an ongoing effort associated with the WMO Commission for Climatology, highlight these anticipated changes, and other key markers of the recent history and current state of climate. Efforts have been made to add to the tabulation of indicators of climate change, including atmosphere (surface temperature, precipitable water, hurricane and typhoon frequencies and mean intensity, Ice Sheet and Glacier Mass Balance), ocean (sea-level time series, ocean stratification, sea ice, ocean heat content and zonal mean temperature upper to ocean), and hydrological (precipitation, PDSI, and Standardized Runoff Index) change. These indicators, and the associated supporting information, characterize both the recent observed history and near-future anticipated change of the earth’s climate and its components. These efforts also begin to show the complexity of different signals at continental and subcontinental scales.
Temperature Changes
The broad agreement of climate models on globally and regionally averaged changes gives confidence in the projected future temperature changes under different IPCC scenarios. Linked to the increase in greenhouse gas concentrations and their radiative effects, there is a general consensus among models that global annual mean surface air temperature will increase during the coming century, assuming no mitigation measures. The warming is due to enhanced greenhouse effect and is generally larger compared to other mechanisms, such as sulfates, which have a cooling effect. Similarly, global surface temperature is also sensitive to the rates of oceanic heat uptake with and feedbacks involving land-surface characteristics and land-use change. This also points to future changes in precipitation due to warming with enhanced greenhouse effect, which is a direct precursor to changing regional or local climate.
Projected changes to global temperatures have important implications for the Earth’s hydrological cycle. When the Earth’s atmosphere is loaded by man-emitted greenhouse gases, there is a clear trend to increase surface air temperature. This response is primarily due to the increased greenhouse effect, and several studies using global climate models (GCMs and ESMs) support this general trend using different models and scenarios with various observed and unobserved changes – in clouds, sea-surface temperature, radiative fluxes, greenhouse gases, and aerosols. Although there are uncertainties due to some aspects of model scenarios and their treatment of clouds that affect the response of the atmospheric hydrological cycle, we will focus on the potential changes in precipitation in most land regions, which are fundamentally a combination of both temperature and vapor changes.
Sea Level Rise
Sea level rise is one of the most robustly projected geophysical changes. Since the early 20th century, people have observed sea level rise along most of the world’s coasts. This rise has occurred by two mechanisms: the expansion of oceans as they warm due to higher global average temperatures and the melting of ice from glaciers, ice caps, and ice sheets. Global mean sea level has recently been rising more rapidly than the individual component contributions. Climate models project future sea level rise by inputting future warming scenarios to reaction pathways for those components. Ice sheets are not as well represented in these models as the ocean and at this time pose a greater projection uncertainty. The ice sheet projections are limited by our understanding of how ice sheets have responded in the geologic past, due to the fact that this response is not perfectly captured in models, or simply because some portion of the process is missing from the models.
The worst-case ice sheet scenario combines maximal volume from polar ice sheets, no delay time, and immediate high emissions rates for the next hundred years, yielding a nearly 5 m sea level rise by 2120. We use the Pliocene epoch to present another possible high-end scenario. Recent work indicates that during the mid-Pliocene, over 15 mya, the Antarctic’s contribution was 16 meters, 4 meters of which was a thermal expansion. If we use maximum “no response” estimate of 16-meter sea level change and assume that 4 m came from the non-ice sheet components, we press 12 m from the ice sheets. We have about 11 new “no response” cases in the literature, all of which are for the United States. These cases do not allow us to truly geographically extrapolate the results, but it is a strong suggestion of the errant estimates methodology. Even without the geologic nor geographic limitations, concede that they only have a sample size of 7 cases and recommend caution in the application of their analyses for a single event. Since these “no response” rates are based on only three time periods with a total of 11 instances, we recommend that risk analyses continue to use the current acceptable input rates, the 20th percentile sea level rise rates.
Extreme Weather Events
Laboratory models can also directly address the intensity and frequency of extremes. The term “extremes” referred to here means defined thresholds of daily temperature or precipitation, wind intensity (e.g., 99th or percentile wind speed), or the onset of large-scale windstorms or rainfall events (e.g., hurricanes or monsoons). These are primarily analyzed for their regional climate change signal, as information on past regional extreme events is only applications-specific at the global level. Changes in extremes are also of primary interest in themselves, since these have great influence socially and economically, including insurance trends, water management, agriculture, public health risks, and energy demand.
It is first discussed what sort of extremes will be presented, followed by specifics on temperature and precipitation extremes. The present Intergovernmental Panel on Climate Change (IPCC) activity is considered, in terms of projected changes in extremes and risk assessment. Finally, the model approach and its limitations will be addressed. The actual impacts analysis of changes in extremes will be the subject of subsequent chapters, but illustrative case studies are used to motivate the discussion in this chapter.
Regional Climate Variability
Considerable concerns have recently been expressed about the vulnerability of specific regions to regional trends in climate variability and change. Questions have been voiced regarding concerns that few explicitly regional aspects of climate have yet been addressed. In the United States, the $3 billion water-resources-related annual damages from extreme climate-related events, concentrated in specific regions of the nation, highlights the critical importance to thousands of federal, regional, and local water-resources agencies of understanding the implications of future regional scales of climate change and variability.
Substantial uncertainties remain about the impact of climate changes on the fragility and/or resilience of many agricultural, water resources, and other systems in specific regions of the United States. For example, several assessment processes that have been performed on the potential impacts of future climate changes on water resources systems have emphasized, on the one hand, the precision with which the American West can be affected, supposedly by large changes in variability, whereas some large water resources systems in the Midwest and East, thought to be sensitive to hydrological changes by others, tended to differ so ambiguously from year to year in terms of estimated future precipitation changes that little useful information was transferred to regional and local policymakers.
Impact of Climate Change on Different Regions
Any global climate model will change the overall trend of future temperature change. The current models are relatively consistent with the results of changes in temperature on a global scale. The regional trends, however, are much less consistent. The prediction of changes in precipitation is even worse, because precipitation is very sporadic in time and space. Sahelian drought, which lasted over 10 years, is a prime example. No climate forecast of any sort has yet been able to predict such an event on the scale of more than a few years. Some models predict an increase in precipitation while others predict a decrease, even if they agree on an increase in temperature. These global models are modified: heat transport in the ocean, built-in temperature increases in models, and forest responses to increased atmospheric carbon dioxide must be considered. Although these points could have been considered, they have generally been ignored or under-represented in previous model discussions.
Mitigation and Adaptation Strategies
Mitigation aims at stemming the flow of greenhouse gases into the atmosphere and thus slowing their concentrations and the global warming that results. To affect a significant change is costly, time-consuming, and requires massive international cooperation and planning that transcends current norms of corporate, social, and political responsibility. Significantly reducing the total emissions from fossil fuel burning would involve not only constraining current practices but also ultimately developing wholly new sources of energy that can replace the abundant energy sources provided by fossil fuels in an economically competitive way. The development of new energy strategies, the implementation of efficient technology transfer to all countries, and the eventual fair sharing of the burdens of constraints are essential tasks of the major global economies of the future.
Mitigation involves several distinct but necessarily interdependent challenges and responses. One step involves world governments, individually and collectively, setting targets on allowable future greenhouse gas emissions and then ensuring that some given distribution of emissions meets that goal. Another step involves an organization at the international level that oversees, revises, and enforces these targets. This cannot be the sort of international organization that has historically been used to enforce pacts like nuclear nonproliferation by holding signers accountable to the organization.
Mitigation Measures
The problem of long-term climate change can indeed be addressed only by stringent control of the emissions of the various greenhouse gases. While it is difficult and very uncertain to predict the impacts of greenhouse gas emissions on human activities and ecosystems over the next few decades, due to the uncertainty about the amount of such emissions and myriad other factors involved, it is generally agreed that, at some point, greenhouse gas emissions will have to be greatly curtailed if undesirable long-term trends in temperature, precipitation, and sea level rise are to be avoided. What is also certain is that there will be great inertia in the world system that will make it difficult to achieve the necessary strictures. There is, in addition, generally a lag time of several decades between imposed changes on emissions and their measurable cause-and-effect influence on the climate system.
Adaptation Strategies
The impacts of climate change and extreme weather events will likely continue to result in consequences that range from minor and localized to severe and widespread. Regardless of the efforts to mitigate global warming, some climate change is inevitable. As a result, society must develop and implement both mitigation and adaptation strategies.
Adaptation strategies fall into several general categories, including mitigation measures (e.g., reduction of greenhouse gas levels), avoidance measures (e.g., not building on active floodplains), defensive measures (e.g., construction of seawalls and dykes for protection against sea level rise and storm surges), institutional measures (e.g., land use policies), and natural systems management (e.g., wetland restoration).
The costs and benefits of a wide range of possible adaptation measures will depend upon the level and speed of climate change. Some experts have argued that the world should wait for more scientifically robust assessments of potential impacts and costs and benefits of alternative responses. In contrast, others have suggested that society cannot afford to wait and should take action now by simultaneously implementing strategies that address climate change and other pressing societal problems such as land use issues. They have suggested that combining measures may slow rates of climate change and buy needed time to develop and implement technology solutions.
The current and likely future socio-economic systems do not place the single high value on reducing climate change that would imply the need for excessive costs on the U.S. economy. However, the assessment’s goal is to demonstrate how reducing emissions can be harmonized with other important goals of world society. As a result, it is important to consider available and technologically feasible ways that can overcome economic disincentives, conflicting interests, desires for energy and economic growth, and behavioral inertia.
