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Climate change is a challenge that requires a broader, whole-of government response. .. I will ensure that the Department of Defense plays its appropriate role within such a response by addressing national security aspects.... Climate change is impacting stability in areas of the world where our troops are operating today. It is appropriate for the Combatant Commands to incorporate drivers of instability that impact the security environment in their areas into their planning.... The effects of a changing climate such as increased maritime access to the Arctic, rising sea levels, desertification, among others impact our security situation. I will ensure that the department continues to be prepared to conduct operations today and in the future, and that we are prepared to address the effects of a changing climate on our threat assessments, resources, and readiness.
James Mattis, Defense Secretary


Climate

Societies and eco-systems have always evolved naturally adapting to the climate. However, fast and deep climate change such as the one forecasted for the next decades will probably have a radical impact on life conditions, and on those activities and economies based on the use of natural resources.

According to a report prepared for the Intergovernmental Panel on Climate Change, rising global temperatures pose an increasing threat to peace and security in the world. Potential for violent conflict could increase, expanding the responsibilities of the defense sector.

Recent observations show that ice sheets can respond to climate warming on decadal time scales and that the Greenland and West Antarctic ice sheets are losing mass at an increasing rate. The largest losses of ice are associated with the acceleration and thinning of large outlet glaciers and ice streams in Greenland and West Antarctica. Although surface atmospheric warming plays a role, ocean warming appears to be the primary driver. Subsurface melting of ice shelves has reduced their buttressing effect, leading to increased discharge of grounded ice. These changes suggest that recent IPCC sea level projections, which exclude large dynamic changes in ice sheets, underestimate the risk of rapid sea level rise.

The potential instability of marine ice sheets (i.e., ice sheets grounded below sea level) is of particular concern. The worlds only large marine ice sheet is the West Antarctic Ice Sheet (WAIS), the collapse of which would raise global sea level by about 5 meters. The WAIS has retreated substantially since the Last Glacial Maximum (LGM) and may have collapsed completely during previous interglacials. On several occasions since the LGM, sea level has risen at rates of more than a meter per century, possibly with significant contributions from Antarctic ice. About a third of the WAIS lies in the Amundsen Sea Embayment (ASE), where outlet glaciers are weakly buttressed by small ice shelves and appear vulnerable to ocean warming. Whether this localized destabilization will yield a full discharge of marine ice from West Antarctica, associated with a global sea-level rise of more than 3 m, or whether the ice loss is limited by ice dynamics and topographic features, is unclear.

Global mean surface temperatures rose rapidly from the 1970s, but have been relatively flat over the 10-15 years to 2013. This prompted speculation that human induced global warming is no longer happening, or at least will be much smaller than predicted. Others maintained that this is a temporary pause and that temperatures will again rise at rates seen previously. The recent pause in global surface temperature rise does not materially alter the risks of substantial warming of the Earth by the end of this century. Nor does it invalidate the fundamental physics of global warming, the scientific basis of climate models and their estimates of climate sensitivity.

A wide range of observed climate indicators continue to show changes that are consistent with a globally warming world, and understanding of how the climate system works. It was not possible to explain the recent lack of surface warming solely by reductions in the total energy received by the planet, i.e. the balance between the total solar energy entering the system and the thermal energy leaving it. Changes in the exchange of heat between the upper and deep ocean appear to have caused at least part of the pause in surface warming, and observations suggest that the Pacific Ocean may play a key role.

When projections from the newer climate models are combined with observations, including those from the first decade of the new century, the uncertainty range for warming out to 2050 is reduced. The very highest values of projected warming are eliminated, but the lower bound is largely unchanged. The most likely warming is reduced by only 10%, indicating that the warming that we might previously have expected by 2050 would be delayed by only a few years.

The 2017 year-to-date temperature across global land and ocean surfaces was 1.69F above the 20th century average of 53.8F. This was the second highest for JanuaryFebruary in the 18802017 record, behind 2016.

El Nino [the child] are a global climate phenomenon that occurs at irregular times, approximately every two to seven years. During an El Nino, surface ocean temperatures in the eastern Pacific off the coast of South America become warmer than usual. The warming trend begins around Christmas time. The following year, in the fall, sea surface temperatures also warm, if somewhat less, in the western Pacific, leading to extreme weather events like flooding and droughts, conditions that are ripe for cholera outbreaks.

The incidence of cholera increased in countries in East Africa, because El Nino can lead to surface flooding that washes contamination into drinking water in areas where theres open defecation. It also can lead to overflowing of sewer systems in urban areas which again can lead to contamination of drinking water.

The issue of climate justice cannot be ignored. Countries that have contributed the least to climate change are paradoxically those that will suffer the most from its impacts. The core challenge is that climate change threatens to overburden states and regions which are already fragile and conflict prone.

The Earth's climate has changed throughout history. Just in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 7,000 years ago marking the beginning of the modern climate era and of human civilization. Most of these climate changes are attributed to very small variations in Earths orbit that change the amount of solar energy our planet receives.

Ninety-seven percent of climate scientists agree that climate-warming trends over the past century are very likely due to human activities, and most of the leading scientific organizations worldwide have issued public statements endorsing this position. The current warming trend is of particular significance because most of it is very likely human-induced and proceeding at a rate that is unprecedented in the past 1,300 years.

Scientists have high confidence that global temperatures will continue to rise for decades to come, largely due to greenhouse gases produced by human activities. The Intergovernmental Panel on Climate Change (IPCC), which includes more than 1,300 scientists from the United States and other countries, forecasts a temperature rise of 2.5 to 10 degrees Fahrenheit over the next century. According to the IPCC, the extent of climate change effects on individual regions will vary over time and with the ability of different societal and environmental systems to mitigate or adapt to change.

All three major global surface temperature reconstructions show that Earth has warmed since 1880. Most of the warming occurred in the past 35 years, with 15 of the 16 warmest years on record occurring since 2001. The year 2015 was the first time the global average temperatures were 1 degree Celsius or more above the 1880-1899 average. The oceans have absorbed much of this increased heat, with the top 700 meters (about 2,300 feet) of ocean showing warming of 0.302 degrees Fahrenheit since 1969.

Causes

Natural drivers of climate cannot explain the recent observed warming. Over the last five decades, natural factors (solar forcing and volcanoes) alone would actually have led to a slight cooling. Even though the 2000s witnessed a solar output decline resulting in an unusually deep solar minimum in 2007-2009, surface temperatures continue to increase.

Earth-orbiting satellites and other technological advances have enabled scientists to see the big picture, collecting many different types of information about Earth and its climate on a global scale. This body of data, collected over many years, reveals the signals of a changing climate.

The heat-trapping nature of carbon dioxide and other gases was demonstrated in the mid-19th century. Their ability to affect the transfer of infrared energy through the atmosphere is the scientific basis of many instruments flown by NASA. There is no question that increased levels of greenhouse gases must cause the Earth to warm in response.

Ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers show that the Earths climate responds to changes in greenhouse gas levels. They also show that in the past, large changes in climate have happened very quickly, geologically-speaking: in tens of years, not in millions or even thousands.

Consequences

The IPCC predicts that increases in global mean temperature of less than 1.8 to 5.4 degrees Fahrenheit (1 to 3 degrees Celsius) above 1990 levels will produce beneficial impacts in some regions and harmful ones in others. Net annual costs will increase over time as global temperatures increase. "Taken as a whole," the IPCC states, "the range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time."

Vector-borne diseases continue to contribute significantly to the global burden of disease, and cause epidemics that disrupt health security and cause wider socioeconomic impacts around the world. All are sensitive in different ways to weather and climate conditions, so that the ongoing trends of increasing temperature and more variable weather threaten to undermine recent global progress against these diseases.

The WHO estimates that one-sixth of the illness and disability suffered worldwide is owing to vector-borne diseases, with more than half of the world's population currently at risk. Every year, more than one billion people are infected, and more than one million people die from vector-borne diseases, including malaria, dengue, schistosomiasis, leishmaniasis, Chagas disease and African trypanosomiasis.

The burden of climate-sensitive diseases is greatest for the poorest populations. For example, the per capita mortality rate from vector-borne diseases is almost 300 times greater in developing nations than in developed regions, both because vector-borne diseases are more common in the tropical climates of many developing countries, and also because of low levels of socioeconomic development and coverage of health services in these areas. In addition, vector-borne disease risks are typically much greater for poor individuals within any population owing to poorer environmental and social conditions.

Vector-borne diseases are among the most well studied of the diseases associated with climate change, owing to their large disease burden, widespread occurrence and high sensitivity to climatic factors. It is not surprising that there is abundant observational evidence of the effects of meteorological factors, from seasonal and interannual patterns of disease incidence in specific locations, to the strong explanatory power of climate variables in accounting for the geographical distribution of most, if not all, vector-borne diseases.

The complexity of these interactions means that the effect of climate change, and the nature and extent of interaction with non-climate factors, varies markedly by diseases and by location.

The length of the frost-free season (and the corresponding growing season) has been increasing nationally since the 1980s, with the largest increases occurring in the western United States, affecting ecosystems and agriculture. Across the United States, the growing season is projected to continue to lengthen. In a future in which heat-trapping gas emissions continue to grow, increases of a month or more in the lengths of the frost-free and growing seasons are projected across most of the U.S. by the end of the 21st century, with slightly smaller increases in the northern Great Plains. The largest increases in the frost-free season (more than eight weeks) are projected for the western US, particularly in high elevation and coastal areas.

Global sea level rose about 17 centimeters (6.7 inches) in the last century. The rate in the last decade, however, is nearly double that of the last century. Global sea level has risen by about 8 inches since reliable record keeping began in 1880. It is projected to rise another 1 to 4 feet by 2100. This is the result of added water from melting land ice and the expansion of seawater as it warms. In the next several decades, storm surges and high tides could combine with sea level rise and land subsidence to further increase flooding in many of these regions. Sea level rise will not stop in 2100 because the oceans take a very long time to respond to warmer conditions at the Earths surface. Ocean waters will therefore continue to warm and sea level will continue to rise for many centuries at rates equal to or higher than that of the current century.

Beaches also erode as sea level rises. A higher ocean level makes it more likely that storm waters will wash over a barrier island or open new inlets. As sea level rises, salt water can mix farther inland or upstream in bays, rivers, and wetlands. Because water on the surface is connected to ground water, salt water can also intrude into aquifers near the coast. Soils may become too salty for farms or forests.

The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA's Gravity Recovery and Climate Experiment show Greenland lost 150 to 250 cubic kilometers (36 to 60 cubic miles) of ice per year between 2002 and 2006, while Antarctica lost about 152 cubic kilometers (36 cubic miles) of ice between 2002 and 2005.

The intensity, frequency and duration of North Atlantic hurricanes, as well as the frequency of the strongest (Category 4 and 5) hurricanes, have all increased since the early 1980s. The relative contributions of human and natural causes to these increases are still uncertain. Hurricane-associated storm intensity and rainfall rates are projected to increase as the climate continues to warm.

Heat waves are periods of abnormally hot weather lasting days to weeks. Heat waves have generally become more frequent across the U.S. in recent decades, with western regions (including Alaska) setting records for numbers of these events in the 2000s. Tree ring data suggests that the drought over the last decade in the western U.S. represents the driest conditions in 800 years. Most other regions in the country had their highest number of short-duration heat waves in the 1930s, when the multi-year severe drought of the Dust Bowl period, combined with deleterious land-use practices, contributed to the intense summer heat through depletion of soil moisture and reduction of the moderating effects of evaporation. However, the recent prolonged (multi-month) extreme heat has been unprecedented since the start of reliable instrumental records in 1895.

In some areas, prolonged periods of record high temperatures associated with droughts contribute to dry conditions that are driving wildfires.



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