Past Climate Change

he Earth's climate has changed throughout history. From glacial periods (or "ice ages") where ice covered significant portions of the Earth to interglacial periods where ice retreated to the poles or melted entirely - the climate has continuously changed.

Scientists have been able to piece together a picture of the Earth's climate dating back decades to millions of years ago by analyzing a number of surrogate, or "proxy," measures of climate such as ice cores, boreholes, tree rings, glacier lengths, pollen remains, and ocean sediments, and by studying changes in the Earth's orbit around the sun.

This page contains information about the causes of climate change throughout the Earth's history, the rates at which the climate has changed, as well as information about climate change during the last 2,000 years.
Causes of Change Prior to the Industrial Era (pre-1780)

Known causes, “drivers” or “forcings” of past climate change include:

* Changes in the Earth's orbit: Changes in the shape of the Earth's orbit (or eccentricity) as well as the Earth's tilt and precession affect the amount of sunlight received on the Earth's surface. These orbital processes -- which function in cycles of 100,000 (eccentricity), 41,000 (tilt), and 19,000 to 23,000 (precession) years -- are thought to be the most significant drivers of ice ages according to the theory of Mulitin Milankovitch, a Serbian mathematician (1879-1958). The National Aeronautics and Space Administration's (NASA) Earth Observatory offers additional information about orbital variations and the Milankovitch Theory.
* Changes in the sun's intensity: Changes occurring within (or inside) the sun can affect the intensity of the sunlight that reaches the Earth's surface. The intensity of the sunlight can cause either warming (for stronger solar intensity) or cooling (for weaker solar intensity). According to NASA research, reduced solar activity from the 1400s to the 1700s was likely a key factor in the “Little Ice Age” which resulted in a slight cooling of North America, Europe and probably other areas around the globe. (See additional discussion under The Last 2,000 Years.)
* Volcanic eruptions: Volcanoes can affect the climate because they can emit aerosols and carbon dioxide into the atmosphere.
o Aerosol emissions: Volcanic aerosols tend to block sunlight and contribute to short term cooling. Aerosols do not produce long-term change because they leave the atmosphere not long after they are emitted. According to the United States Geological Survey (USGS), the eruption of the Tambora Volcano in Indonesia in 1815 lowered global temperatures by as much as 5ºF and historical accounts in New England describe 1816 as “the year without a summer.”
o Carbon dioxide emissions: Volcanoes also emit carbon dioxide (CO2), a greenhouse gas, which has a warming effect. For about two-thirds of the last 400 million years, geologic evidence suggests CO2 levels and temperatures were considerably higher than present. One theory is that volcanic eruptions from rapid sea floor spreading elevated CO2 concentrations, enhancing the greenhouse effect and raising temperatures. However, the evidence for this theory is not conclusive and there are alternative explanations for historic CO2 levels (NRC, 2005). While volcanoes may have raised pre-historic CO2 levels and temperatures, according to the USGS Volcano Hazards Program, human activities now emit 150 times as much CO2 as volcanoes (whose emissions are relatively modest compared to some earlier times).

These climate change “drivers” often trigger additional changes or “feedbacks” within the climate system that can amplify or dampen the climate's initial response to them (whether the response is warming or cooling). For example:

* Changes in greenhouse gas concentrations: The heating or cooling of the Earth's surface can cause changes in greenhouse gas concentrations. For example, when global temperatures become warmer, carbon dioxide is released from the oceans. When changes in the Earth's orbit trigger a warm (or interglacial) period, increasing concentrations of carbon dioxide may amplify the warming by enhancing the greenhouse effect. When temperatures become cooler, CO2 enters the ocean and contributes to additional cooling. During at least the last 650,000 years, CO2 levels have tended to track the glacial cycles (IPCC, 2007). That is, during warm interglacial periods, CO2 levels have been high and during cool glacial periods, CO2 levels have been low (see Figure 1).

This graph shows CO2 concentrations from 647,000 BC to 2006 AD, and Antarctic temperatures from 421,000 BC to 2000 AD. (Antarctic temperature is measured as the change from average conditions for the period 1850 AD to 2000 AD.) The graph shows a fairly close relationship between CO2 concentrations and temperature during the period when both CO2 and temperature are available, and shows a sharp increase in CO2 concentrations during the 20th century.

Figure 1: Fluctuations in temperature (red line) and in the atmospheric concentration of carbon dioxide (yellow) over the past 649,000 years. The vertical red bar at the end is the increase in atmospheric carbon dioxide levels over the past two centuries and before 2007. Click on thumbnail for a full-size image and references.

* Changes in ocean currents: The heating or cooling of the Earth's surface can cause changes in ocean currents. Because ocean currents play a significant role in distributing heat around the Earth, changes in these currents can bring about significant changes in climate from region to region.

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Rates of Change

Studies of the Earth's previous climate suggest periods of stability as well as periods of rapid change. Recent climate research suggests:

* Interglacial climates (such as the present) tend to be more stable than cooler, glacial climates. For example, the climate during the current and previous interglacials (known as the Holocene and Eemian interglacials) has been more stable than the most recent glacial period (known as the Last Glacial Maximum). This glacial period was characterized by a long string of widespread, large and abrupt climate changes (NRC, 2002).
* Abrupt or rapid climate changes tend to frequently accompany transitions between glacial and interglacial periods (and vice versa). For example, a significant part of the Northern Hemisphere (particularly around Greenland) may have experienced warming rates of 14-28ºF over several decades during and after the most recent ice age (IPCC, 2007).

While abrupt climate changes have occurred throughout the Earth's history, human civilization arose during a period of relative climate stability.

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The Last 2,000 Years

During the last 2,000 years, the climate has been relatively stable. Scientists have identified three departures from this stability, known as the Medieval Climate Anomaly (also referred to as the Medieval Warm Period), the Little Ice Age and the Industrial Era:

* The Medieval Climate Anomaly: Between roughly 900 and 1300 AD, evidence suggests Europe, Greenland and Asia experienced relative warmth. While historical accounts and other evidence document the warmth that occurred in some regions, the geographical extent, magnitude and timing of the warmth during this period is uncertain (NRC, 2006). The American West experienced very dry conditions around this time.
* The Little Ice Age: A wide variety of evidence supports the global existence of a "Little Ice Age" (this was not a true "ice age" since major ice sheets did not develop) between about 1500 and 1850 (NRC, 2006). Average temperatures were possibly up to 2ºF colder than today, but varied by region.
* The Industrial Era: An additional warm period has emerged in the last 100 years, coinciding with substantially increasing emissions of greenhouse gases from human activities (see Recent Climate Change for more information).

Prior to the Industrial Era, the Medieval Climate Anomaly and Little Ice Age had defined the upper and lower boundaries of the climate's recent natural variability and are a reflection of changes in climate drivers (the sun's variability and volcanic activity) and the climate's internal variability (referring to random changes in the circulation of the atmosphere and oceans).

The issue of whether the temperature rise of last 100 years crossed over the warm limit of the boundary defined by the Medieval Climate Anomaly has been a controversial topic in the science community. The National Academy of Sciences recently completed a study to assess the efforts to reconstruct temperatures of the past one to two millennia (see Figure 2) and place the Earth's current warming in historical context (NRC, 2006).
Figure 2. This graph provides reconstructions of Northern Hemisphere average or global average surface temperature variations over the last 1,100 years from six research teams, along with the instrumental record of global average surface temperature. Overall, the curves show a warming around 1000 AD followed by a long general cooling trend that continues until the early 1900s. Each curve illustrates a somewhat different history of temperature changes, with a range of uncertainties that tend to increase backward in time.

Figure 2: Reconstructions of (Northern Hemisphere average or global average) surface temperature variations from six research teams (in different color shades) along with the instrumental record of global average surface temperature (in black). Each curve illustrates a somewhat different history of temperature changes, with a range of uncertainties that tend to increase backward in time (as indicated by the shading). Reference: NRC, 2006. (Figure reprinted with permission from Surface Temperature Reconstructions© (2006) by the National Academy of Sciences, Courtesy of the National Academies Press Exit EPA Disclaimer, Washington, D.C.)

According to the study Exit EPA Disclaimer (NRC, 2006):

* There is a high level of confidence that the global average temperature during the last few decades was warmer than any comparable period during the last 400 years.
* Present evidence suggests that temperatures at many, but not all, individual locations were higher during the past 25 years than any period of comparable length since A.D. 900. However, uncertainties associated with this statement increase substantially backward in time.
* Very little confidence can be assigned to estimates of hemisphere average or global average temperature prior to A.D. 900 due to limited data coverage and challenges in analyzing older data.

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References

* IPCC, 2007: Climate Change 2007: The Physical Science Basis. Exit EPA DisclaimerContribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning (eds.)].
* National Research Council (NRC), 2002: Abrupt Climate Change, Inevitable Surprises. Exit EPA Disclaimer National Academy Press, Washington, DC. National Academy Press, Washington, DC
* National Research Council (NRC), 2005: Radiative Forcing of Climate Change. Exit EPA Disclaimer National Academy Press, Washington, DC. National Academy Press, Washington, DC

Will Big Business Save the Earth?

HERE is a widespread view, particularly among environmentalists and liberals, that big businesses are environmentally destructive, greedy, evil and driven by short-term profits. I know — because I used to share that view.

But today I have more nuanced feelings. Over the years I’ve joined the boards of two environmental groups, the World Wildlife Fund and Conservation International, serving alongside many business executives.

As part of my board work, I have been asked to assess the environments in oil fields, and have had frank discussions with oil company employees at all levels. I’ve also worked with executives of mining, retail, logging and financial services companies. I’ve discovered that while some businesses are indeed as destructive as many suspect, others are among the world’s strongest positive forces for environmental sustainability.

The embrace of environmental concerns by chief executives has accelerated recently for several reasons. Lower consumption of environmental resources saves money in the short run. Maintaining sustainable resource levels and not polluting saves money in the long run. And a clean image — one attained by, say, avoiding oil spills and other environmental disasters — reduces criticism from employees, consumers and government.

What’s my evidence for this? Here are a few examples involving three corporations — Wal-Mart, Coca-Cola and Chevron — that many critics of business love to hate, in my opinion, unjustly.

Let’s start with Wal-Mart. Obviously, a business can save money by finding ways to spend less while maintaining sales. This is what Wal-Mart did with fuel costs, which the company reduced by $26 million per year simply by changing the way it managed its enormous truck fleet. Instead of running a truck’s engine all night to heat or cool the cab during mandatory 10-hour rest stops, the company installed small auxiliary power units to do the job. In addition to lowering fuel costs, the move eliminated the carbon dioxide emissions equivalent to taking 18,300 passenger vehicles off the road.

Wal-Mart is also working to double the fuel efficiency of its truck fleet by 2015, thereby saving more than $200 million a year at the pump. Among the efficient prototypes now being tested are trucks that burn biofuels generated from waste grease at Wal-Mart’s delis. Similarly, as the country’s biggest private user of electricity, Wal-Mart is saving money by decreasing store energy use.

Another Wal-Mart example involves lowering costs associated with packaging materials. Wal-Mart now sells only concentrated liquid laundry detergents in North America, which has reduced the size of packaging by up to 50 percent. Wal-Mart stores also have machines called bailers that recycle plastics that once would have been discarded. Wal-Mart’s eventual goal is to end up with no packaging waste.

One last Wal-Mart example shows how a company can save money in the long run by buying from sustainably managed sources. Because most wild fisheries are managed unsustainably, prices for Chilean sea bass and Atlantic tuna have been soaring. To my pleasant astonishment, in 2006 Wal-Mart decided to switch, within five years, all its purchases of wild-caught seafood to fisheries certified as sustainable.

Coca-Cola’s problems are different from Wal-Mart’s in that they are largely long-term. The key ingredient in Coke products is water. The company produces its beverages in about 200 countries through local franchises, all of which require a reliable local supply of clean fresh water.

But water supplies are under severe pressure around the world, with most already allocated for human use. The little remaining unallocated fresh water is in remote areas unsuitable for beverage factories, like Arctic Russia and northwestern Australia.

Coca-Cola can’t meet its water needs just by desalinizing seawater, because that requires energy, which is also increasingly expensive. Global climate change is making water scarcer, especially in the densely populated temperate-zone countries, like the United States, that are Coca-Cola’s main customers. Most competing water use around the world is for agriculture, which presents sustainability problems of its own.

GLOBAL WARMING

Global climate change impacts in the United States are spelled out with renewed authority in a report released June 16 by the federal government.

The report's key information has been well reported here and in Earth Under Fire and other books, but bears repeating in its straightforward language and up-to-date numbers.

Human activities have led to large increases in heat-trapping gases over the past century. The global warming of the past 50 years is due primarily to this human-induced increase. Global average temperature and sea level have increased, and precipitation patterns have changed.

Human “fingerprints” also have been identified in many other aspects of the climate system, including changes in ocean heat content, precipitation, atmospheric moisture, plant and animal health and location, and Arctic sea ice.

In the U.S., the amount of rain falling in the heaviest downpours has increased approximately 20 percent on average in the past century.

Many types of extreme weather events, such as heat waves and regional droughts, have become more frequent and intense during the past 40 to 50 years. The destructive energy of Atlantic hurricanes has increased... In the eastern Pacific, the strongest hurricanes have become stronger since the 1980s, even while the total number of storms has decreased.

Sea level has risen along most of the U.S. coast over the last 50 years, and will rise more in the future. Arctic sea ice is declining rapidly and this is very likely to continue. Global temperatures are projected to continue to rise over this century.

Whether by 2-3 degrees F or more than 11 degrees depends on a number of factors, including the amount of heat-trapping gas emissions humans continue to allow and how sensitive the climate is to those emissions. Lower emissions of heat-trapping gases will delay the appearance of climate change impacts and
lessen their magnitude.

Unless the rate of emissions is substantially reduced, impacts are expected to become increasingly severe for more people and places.

For more from this report, please go to the Temperate Zone page.

Obama's Climate Team Moves to Regulate Greenhouse Gases as Research Shows Global Warming Continues at High Rates

President Barack Obama's new Environmental Protection Agency chief Lisa Jackson has moved to put CO2 and other greenhouse gases under regulation by the Clean Air Act. In one of the most anticipated early actions by the new Administration, the EPA issued a proposed finding on April 17 that these gases endanger human health and well-being. When made final, this will clear the way for regulation of vehicle exhaust, which is the source of about 30 percent of US carbon dioxide emissions.

This is one of the most visible of the climate actions springing from members of the President's new Cabinet, which includes leading scientists and informed diplomats. As they took their posts, working scientists announced in two international meetings that many factors in rapid global warming were getting worse or running at rates which only a few years ago were thought to be extreme.

Besides Jackson, who an was an experienced state environment leader before taking over at EPA, Obama appointed former EPA head Carol Browner to a new post of White House climate and energy chief; Nobel Prize winner Stephen Chu as Secretary of Energy; Harvard professor John Holdren, who has been outspoken on the dangers of climate disruption, as Presidential science advisor; and acclaimed ocean scientist Jane Lubchenco as head of NOAA.

Secretary of State Hillary Clinton replaced George Bush's footdragging international climate negotiators with a team lead by Todd Stern. One of his first actions was to announce to international climate talks in Bonn that "the science is clear, and the threat is real. The facts on the ground are outstripping the worst case scenarios. The costs of inaction-or inadequate actions-are unacceptable." The Bonn talks are preliminary to crucial UN Climate Convention meetings in Copenhagen in December [[link: http://unfccc.int/2860.php]], at which nations have promised to agree to sharp limits on greenhouse gases, replacing the Kyoto Protocol. Many national issues and roadblocks remain, however, prime of which is the world recession which dominates other international meetings.

The EPA finding, although initially focused directly on vehicle emissions, will lead under the Clean Air Act to regulation of greenhouse gas emissions from power plants, source of nearly half of American CO2. Congress is also proposing control of emissions using a cap and trade process familiar to many from previous Clean Air Act procedures to limit sulphur pollution from coal burning plants. A comprehensive climate and energy bill, drafted by Rep. Henry Waxman of California and Rep. Edward Markey of Massachusetts, will be debated in the House this spring. Reactions to the proposed legislation are being posted by many business and environmental groups and will surely intensify as the bill is amended and moves toward a vote later this year.

The urgency of climate action is even greater now because some recent observations are at or beyond the highest projections of previous reports. Scientific studies updating the IPCC assessment of 2007 show that more CO2 is being put into the air than ever before. Rates of change of global mean temperature, sea level rise, ice sheet changes in Greenland and the edges of Antarctica, and ocean chemical changes are running at the highest projections of the 2007 IPCC. In February 2009 at the annual meeting of the American Association for the Advancement of Science, Dr. Chris Field of the Carnegie Institute also reported that some major ways that the earth naturally absorbs CO2 were less efficient now, leaving more of the gas in the air. I heard him say that because of all this, we are "on a trajectory of climate... that has not been explored."

Not every indication of climate is changing this rapidly, but most scientists now predict a 5 degree F or more temperature increase and at least three feet of sea level rise before 2100 if things continue in this way. The changes documented in these website pages and my book occurred during a time of just over one degree of warming.

Every citizen of the world needs to be aware of rapid climate change:

1. Understand the problem, its causes and threats.
2. Let your leaders know the facts and that you expect them to act.
3. Do something today to reduce greenhouse gas output -- please Take Action


The World View of Global Warming project is documenting this change through science photography from the Arctic to Antarctica, from glaciers to the oceans, across all climate zones. Rapid climate change and its effects is fast becoming one of the prime events of the 21st century. It is real and it is accelerating across the globe. As the effects of this change combine with overpopulation and weather crises, climate disruptions will affect more people than does war

The Importance of Sound Science in Public Policy

Climate scientists—and experts in related fields—will continue their research to refine our understanding of the Earth's complex atmospheric system. However, despite the advances they have made, or perhaps because of them, climate science itself is under increasing attack in some media and policy forums. Ultimately, the best way to improve public understanding of global warming issues and to create a more receptive atmosphere for policy action is for scientists to repeatedly, patiently, and strategically present accurate, credible information to the media and policymakers. UCS's Sound Science Initiative is doing just that.

Part of what scientists must do is to explain why it is unrealistic and unnecessary to expect total scientific certainty before taking appropriate action to address the threat of global warming. As climatologist Stephen Schneider notes,

"I'm not 99 percent sure, but I am 90 percent sure [that the climate is changing]. Why do we need 99 percent certainty when nothing else is that certain? If there were only a 5 percent chance the chef slipped some poison in your dessert, would you eat it?"


In the IPCC's latest assessment report (2007), the scientists drew some very strong conclusions about the present reality of climate change. The Panel concluded, for example, that human-induced warming over recent decades is already affecting many physical and biological processes on every continent. Nearly 90 percent of the 29,000 observational data series examined revealed changes consistent with the expected response to global warming, and the observed physical and biological responses have been greatest in the regions that warmed the most. Examples of observed changes in response to 20th century warming include

* Shrinking glaciers
* Thawing permafrost
* Earlier break-up of river and lake ice
* Lengthening of mid- to high-latitude growing seasons
* Poleward and altitudinal shifts of plant and animal ranges
* Declines of some animal and plant populations
* Earlier tree flowering, insect emergence and egg-laying in birds.

Once we observe the more dramatic changes in response to climate change, by definition, it will be too late to take precautionary measures. And it may even be too late for the most cost-effective remedial measures.

The IPCC's Fourth Assessment Report has made it clear that there are a variety of strategies available today that, if implemented quickly, can rein in global warming and avoid the most severe consequences. The impact of the more ambitious of these strategies on the world economy is expected to be a fraction of a percent reduction in the annual average growth rate of global gross domestic product (GDP).

We also need strategies to cope with those consequences of global warming that are already unavoidable due to past emissions. Adaptation strategies are necessary to supplement climate change mitigation efforts.

While IPCC reports are not policy-prescriptive, the analysis they provide is highly policy-relevant. IPCC reports are strong evidence that scientists' voices can make a difference in the public debate and in public policy to address this global problem.

Global Warming

Easier - The surface of the earth has been warming, the average temperature increasing, for several years. People studying this do not agree on the cause of the warming trend. Some say that man has caused the change; others claim that it is a natural trend.

Harder - For several years believers and skeptics have argued about the causes of global warming. The problem is complicated because believers warn that man-made causes if left to advance too far may be irreversible. Reduction of the rainforests, continued growth in hydrocarbon industries, increases in livestock, and depletion of the ozone are all considered factors in the debate. Skeptics maintain that the climate change is a natural phenomenon, that man's effect on nature is largely overrated. The fact is that for several years, the earth's temperature is rising. The problem remains in deciding what if anything we can do about it.


Earth on Fire (NASA Classroom of the Future™)

http://www.cotf.edu/ete/modules/carbon/earthfire.html
Are our industrial and agricultural practices changing Earth's climate? You'll examine humankind's impact on the global environment as well as Earth's past in an attempt to answer this important question.


Global Warming at the U.S. Environmental Protection Agency

http://www.epa.gov/globalwarming/
This site presents information on the very broad issue of climate change and global warming.
Similar Websites:
2) Global Warming/Climate Change Theme Page at Community Learning Network
http://www.cln.org/themes/global_warming.html
3) Global Warming at Environmental Defense http://www.edf.org/programs/GRAP/
4) Global Warming Central at Pace University
http://www.law.pace.edu/env/energy/globalwarming.html


Global Warming at Skepticism.Net

http://www.skepticism.net/global_warming/index.html
If some environmentalists are to be believed, we are on the verge of massive global climate change which will see a significant rise in sea levels, chaotic weather patterns, and catastrophic droughts all caused by small increase in global average temperature. This site provides links to resources skeptical of those sort of doomsday scenarios.

Greenhouse gases are air pollutants under the Clean Air Act: U.S. policy on global warming today

The Supreme Court ordered the federal government today to take a fresh look at regulating carbon dioxide emissions from cars. In a 5-4 decision, the court said the Clean Air Act gives the Environmental Protection Agency the authority to regulate the emissions of carbon dioxide and other greenhouse gases from cars. Greenhouse gases are air pollutants under the landmark environmental law, Justice John Paul Stevens said in his majority opinion. The case is Massachusetts v. EPA, 05-1120.

Greenhouse gases, flowing into the atmosphere and oceans at an unprecedented rate, are leading to larger extreme climatic events, rising sea levels and other marked ecological changes.

The politics of global warming have changed dramatically since the court agreed last year to hear its first global warming case. Business leaders are saying they are increasingly open to congressional action to reduce greenhouse gases emissions, of which carbon dioxide is the largest. Carbon dioxide is produced when fossil fuels such as oil and natural gas are burned.

The court had three questions before it.

1. Do states have the right to sue the EPA to challenge its decision?
2. Does the Clean Air Act give EPA the authority to regulate tailpipe emissions of greenhouse gases?
3. Does EPA have the discretion not to regulate those emissions?

The court said yes to the first two questions. On the third, it ordered EPA to re-evaluate its contention it has the discretion not to regulate tailpipe emissions. The court said the agency has so far provided a "laundry list" of reasons that include foreign policy considerations. The majority said the agency must tie its rationale more closely to the Clean Air Act.

The decision also is expected to boost California's prospects for gaining EPA approval of its own program to limit tailpipe emissions of greenhouse gases. Federal law considers the state a laboratory on environmental issues and gives California the right to seek approval of standards that are stricter than national norms.

(Source: GWIC)

Electric Cars as Barack's NEW Strategy for Transportation fuels

Plug-in hybrids (and electric cars) are an essential climate strategy. The U.S. has just enacted the Energy Improvement and Extension Act of 2008 as part of the bailout of the U.S. financial system. The law provides tax credits for purchases of plug-in hybrid vehicles until less than a year after the first 250,000 are sold, worth $2,500 plus $417 for each kilowatt-hour of battery capacity over 4 kilowatt-hours, up to $7,500 for cars under 10,000 pounds (4536 kg), or more for larger vehicles.

BYD Auto is the Chinese company that last fall launched the very first mass-production plug-in hybrid in the world. It will display both its F3DM plug-in hybrid sedan, and a new E6 electric crossover vehicle. Executives will describe its lithium iron phosphate cells, and the Dual Mode plug-in hybrid system. BYD might be dismissed as just another Chinese car company (there are several dozen), except that famed investor Warren Buffet acquired a 10-percent stake in its parent company last September. The car company is a subsidiary of BYD Company Ltd., the world's second largest producer of rechargeable batteries—unlike GM, which has to buy its cells from other companies.
(GWIC-IPCC)