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I think that measuring with precision human activity on the climate is something very challenging to do and theres tremendous disagreement about the degree of impact. So no, I would not agree that its a primary contributor to the global warming that we see. But we dont know that yet, we need to continue to debate, continue the review and analysis.
Scott Pruitt, US Environmental Protection Agency Administrator

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


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.

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.

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.

In November 2012, Donald Trump tweeted that global warming is a Chinese hoax. He said that it's part of a plot designed to bring down US business and manufacturing. "The concept of global warming was created by and for the Chinese in order to make U.S. manufacturing non-competitive." He said he wants to dismantle the USA's involvement in the Paris Climate Agreementt a pledge between world leaders to stop the earth heating up more than 2 degrees Celsius because it is "bad for US business."

Since then, he was on both sides of the issue. After the election, he admitted there is some connectivity between human activity and climate change. Oklahoma attorney general Scott Pruitt was Donald Trumps pick to head of the Environmental Protection Agency. The Editorial Board of The New York Times wrote "Pruitt has repeatedly suggested that the science of climate change is far from settled, when in fact it is, and says that scientists continue to disagree about whether there is a relationship between human activity and rising atmospheric temperatures, which they dont."

Donald Trump has proposed reducing the budget of the National Oceanic and Atmospheric Administration, the Washington Post reported 04 March 2017. The cuts to the NOAA could affect research, eliminate smaller initiatives and leave 3,000 people out of work. The Commerce Department agency "would be hit by an overall 18 percent reduction," the Post reports. NOAA's satellite data division would lose 22 percent of its funding, or $513 million (483 million euros). However, an unnamed White House official cautioned the paper against reporting specific numbers during the "evolving" process.

The AP reported that Trump plans to reduce the Environmental Protection Agency's staff by 20 percent now that campaign loyalist Scott Pruitt - who sued the EPA over regulations 14 times as Oklahoma's attorney general - has taken charge. Trump planned to fund beefed-up military spending through massive cuts to domestic agencies and departments.

The New York Times reported deep divisions within Trump's team ahead of an imminent decision on the US's participation in the Paris agreement. Energy and government officials told the newspaper that senior adviser Steve Bannon has pressed Trump to quit the historic agreement, which 194 countries reached in December 2015 to fight global warming by reducing greenhouse gas emissions. Former ExxonMobil CEO and current US Secretary of State Rex Tillerson rejected Bannon's position, the Times reported, as had Trump's more influential daughter, Ivanka.

In their book, "Merchants of Doubt", historians Naomi Oreskes and Erik Conway explain how a looseknit group of high-level scientists, with extensive political connections, ran effective campaigns to mislead the public and deny well-established scientific knowledge over four decades. In seven compelling chapters addressing tobacco, acid rain, the ozone hole, global warming, and DDT, Oreskes and Conway show how the ideology of free market fundamentalism, aided by a too-compliant media, has skewed public understanding of some of the most pressing issues.

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.


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.


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."

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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