Accumulating Heat

The earth has warmed rapidly over the past century due mainly to human activity, and especially over the past few decades. The increased greenhouse effect has warmed the land and air and melted ice, but most of it (about 90%) has gone into heating the oceans. Several Skeptical Science contributors worked together to publish a scientific paper1 which combined the land, air, ice, and ocean warming data. It found that for recent decades the earth has been heating at a rate of 250 trillion Joules per second.

“Joules per second” is a difficult unit of measure to appreciate, and is especially foreign to people who are unfamiliar with science. This widget attempts to put that heating into terms that are easier to visualize. 250 trillion Joules per second is equivalent to:

	Detonating four Hiroshima atomic bombs per second
	Experiencing two Hurricane Sandys per second
	Enduring four 6.0 Richter scale earthquakes per second
	Being struck by 500,000 lightning bolts per second
	Exploding more than eight Big Ben towers, with every inch packed full of dynamite, per second

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Climate Heat Carbon Dioxide Impacts

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The Climate and Heat

The earth's climate system absorbs heat in many different ways. Increases in the temperatures that people experience day to day are only one of several reservoirs for accumulating heat. While changes in the atmosphere are the easiest to recognize, they are also the most variable and subject to “noise”. Changes in the ocean, where most of the heat is going, have been more steady, while the melting of vast stores of ice is accelerating. The earth continues to warm, day after day, at a concerning rate.

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Ocean Atmosphere Land Melting Ice Trends

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Climate Trends

When the energy from all of the earth's “heat” reservoirs is combined, the clear, decades long trend is unequivocal and staggering. With the exception of short “hiatus” periods, the earth has been gaining heat, virtually continuously, at an average rate of 250 trillion Joules per second, and this trend shows no serious sign of ending.

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Greenhouse Gases

Without greenhouse gases, the temperature at the surface of the earth would be a mere -15°C (5°F). Life on earth is made possible by greenhouse gases.

The earth's atmosphere is mostly transparent to incoming sunlight, which passes through and warms the surface of the earth. Warm objects in turn emit another wavelength of light, one invisible to the human eye, termed “infrared radiation”. Like visible light, infrared radiation passes through the atmosphere and into space.

But small traces of greenhouse gases, such as carbon dioxide, are not transparent to infrared radiation. They absorb and re-emit that energy, trapping some of that heat within the atmosphere.

Changes Fingerprints 450 ppm Back

Climate Changes

Changes in the climate are visible all around us. Some are subtle and seemingly inconsequential, but these changes are accelerating and undeniable.

Spring comes earlier. Tree lines and species are migrating poleward and upward. Glaciers and Arctic ice are retreating at an alarming rate4. Sea levels are rising5. Every day, more and more studies point towards a changing and warming world in new and sometimes unexpected ways.

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Climate Change Fingerprints

The indicators that recent climate change is the result of burning fossil fuels, rather than from some unknown natural variation, are clear and consistent with what we do know.

There are subtle differences to how the world will warm due to greenhouse gases compared with other potential sources (such as an increase in the warmth of the sun). Most importantly, scientists know that greenhouse gases would cause the upper atmosphere to cool rather than warm.

We also know that the source of the additional carbon dioxide in the atmosphere is due to burning fossil fuels. The carbon in fossil fuels differs from atmospheric carbon because it has less of the isotope known as ¹³C (Carbon-13), a heavier-than-normal version of carbon. Plants generally prefer the lighter and more common ¹²C (Carbon-12) for photosynthesis, so fossil fuels, which are produced from decayed plant matter, are deficient in ¹³C. As a result, when we burn fossil fuels we cause the percentage of 13C in the atmosphere to drop, and this change has been detected.

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450 ppm

Scientists have established that climate change greater than 2°C (4°F) will likely be extremely dangerous. We are likely to have committed our planet to that degree of warming when atmospheric carbon dioxide concentrations reach 450 ppm (parts per million). The natural, pre-industrial level of carbon dioxide (CO₂) was around 285 ppm. The level of CO₂ is currently near 400 ppm.

That level of carbon dioxide, 400 ppm, has not been seen in the atmosphere for millions of years.

At the current rate, adding 2 ppm per year, we will reach 450 ppm around the year 2038, a mere 25 years from now.

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Impacts of Climate Change

Not all effects of climate change can be anticipated, and not all effects that are anticipated may come to pass, but the number of expected, negative impacts on human society present a clear and worrying danger.28 Some of these impacts are already being felt, to varying degrees, although many will not seriously present themselves until temperatures increase by 2°C or more (although we have already committed to more than 1.4°C of warming, depending on actual climate sensitivity).

• Ecosystem changes, species range shifts and extinctions
• Threats to food supplies
• Threats to water supplies
• Increased and more frequent damage from storms, fires and floods
• Changes and increases in disease vectors
• Increased morbidity and mortality from heat waves, floods and droughts

It is important to realize that no matter how strong these impacts are felt now, they will grow worse over time, and when they do, we will have no ability to reverse any of them.

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Ocean Heat

More than 90% of all heat being absorbed by the earth, each and every day, is going into the oceans.

The ocean, when viewed from a climate perspective, is often considered in three layers:

• The surface to 700 meters down.
• 700 meters to 2000 meters down.
• 2000 meters down to the bottom (average is about 3800 meters).

For some time, scientists believed that ocean warming would be restricted to the upper 700 meters and that global warming would take a very long time to penetrate deeper than that. Recent studies2 and modern measurement techniques have shown, however, that the ocean below 700 meters is heating as well, and the amount of energy that it takes to do so is staggerring.

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The Ocean: How We Know

Scientists2 use ocean heat content measurements from ARGO floats, as well as data from expendable bathythermographs (XBT) and mechanical bathythermographs (MBT).

Argo is an international project to collect information on the temperature and salinity of the upper part of the world's oceans. Argo uses robotic floats that spend most of their life drifting below the ocean surface, reaching depths of 2000m and spending periods of approximately 10 days below the surface. Floats take temperature and salinity measurements as they rise to the surface. After surfacing they transmit their data to satellites and then submerge to repeat the data collection cycle. Currently, there are roughly 3000 floats producing 100,000 temperature/salinity profiles per year.

A bathythermograph is an instrument which has a temperature sensor and is thrown overboard from ships to record pressure and temperature changes as it drops through the water. These were the main instruments used to measure OHC before the ARGO float network was deployed starting about a decade ago to provide more accurate and consistent data.

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The Ocean: What We Know

• The ocean accounts for more than 90% of the heat absorbed by the earth in the past 30 years.
• The total increase in heat content of the oceans over the period from 1955-2010 was 24 x 10²² (240,000,000,000,000,000,000,000) Joules.
• The energy absorbed by the oceans will not quickly dissipate.
• As the ocean warms it expands, leading to marked sea level rise.
• Increased ocean temperatures help to warm the atmosphere.
• Increased ocean temperatures help to generate and intensify storms.
• Warmer waters, combined with ocean acidification, are pushing some forms of marine life beyond their limits.

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The Atmosphere

Changes in the temperature of the earth's atmosphere are the easiest to measure and the most obvious in an individual's personal experience, but the atmosphere is also the most variable. One very warm year can be followed by several cold ones, while one region may experience an unusual cold snap while many other parts of the globe endure record warmth. Many factors can influence global atmospheric temperatures over short time frames of a few years, which in turn disguises the insistent, uninterrupted warming which is occurring overall.

Nevertheless, the atmosphere has warmed by 0.8°C (1.4°F) in the past century. This warming is more exaggerated at the poles, leading to even greater swings in temperatures further from the equator. Yet it still accounts for only 2% of total heat absorbed by the earth's climate.

Variability What We Know How We Know Back

Variability

Scientists and statisticians have worked together to try to quantify and eliminate the most obvious forms of variability in global atmospheric temperatures by using standard statistical methods. In one study6, the authors found that after removing the influence of the most significant three factors (ENSO events, solar variations, and aerosols) the seemingly chaotic, drunken meanderings of the earth's temperature straightened into a clear, steady increase in global temperatures.

In particular, in the past decade, a quiet sun, an increase in La Niña (cold) events, and an increase in aerosols have worked to temporarily slow global warming. This sort of hiatus period is often seen in climate models, when negative factors happen to combine to temporarily overwhelm the global warming signal. It is clear, however, from the evidence that any respite is temporary.

The atmosphere, ocean, land and ice continue to absorb heat, and global warming is going to continue well into our future.

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ENSO Events

The Pacific is not only the world's largest ocean, but it also boasts by far the largest expanse of water along the equator, where the sun's rays are strongest. Periodic events, termed El Niño and La Niña, lead to three common states in the equatorial regions of the Pacific. These states in turn affect air temperatures and precipitaiton around the globe, and so are keys to understanding and predicting short-term climate variations.

• El Niño events denote the spread of warmer than usual waters across much of the equatorial Pacific. This raises temperatures globally.
• La Niña events denote the piling up of warmer waters in the western Pacific and the spread of cooler than usual waters across the eastern Pacific, off the coast of South America. This reduces temperatures globally.
• ENSO neutral conditions, when neither an El Niño nor a La Niña is present, is the third state.

One way to view temperature changes without the confusing influences of ENSO events is to compare apples to apples. Compare all El Niño events to each other, La Niña to each other, and neutral conditions. When this is done, again, the constant, upward trend in global temperatures becomes clear.

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Solar Variability

The sun supplies virtually all of the energy that fuels the earth's climate, but changes in solar activity are necessary to account for changes in the earth's climate. While the sun did warm slightly in the early part of the Twentieth century, it has since begun to quiet again. These minor changes in solar output, however, are not nearly strong enough to account for warming this century, although they do contribute somewhat to dampening recent anthropogenic warming. A “hot” sun, for example, emits roughly 1367 Watts/meter², while a “cool” sun emits 1365.5 Watts/meter², a difference between “hot” and “cold” of only about one tenth of one percent.

One study7 used a statistical test on the temperature data, and found that while solar activity can account for about 11% of the global warming from 1889 to 2006, it can only account for 1.6% of the warming from 1955 to 2005, and had a slight cooling effect (-0.004°C per decade) from 1979 to 2005. Multiple other studies 6 8 9 confirm this conclusion.

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Aerosols

Volcanoes emit sulfate aerosols which reflect incoming sunlight, cooling the planet. A large volcanic eruption such as the Pinatubo eruption in 1991 can have a global cooling effect of 0.1°–0.3°C (0.18°–0.54°F) for several years 10.

However, mega-eruptions or a series of eruptions can have a cooling effect that take decades to wear off, giving a perceived warming effect as temperatures return to normal. Scientists have studied past volcanoes11, particularly over the past few centuries, and found that early 20^th century warming resulted, in part, from a recovery from earlier periods of heavy vulcanism. In short, a lack of volcanic activity had some part in temperature rise over the first half of the 20^th century. However, it has played little part in the modern global warming trend that began in the 1970s.

More recently, in the past decade, scientists12 have found that the increase in greenhouse gases was exceeded by an even greater increase in sunlight-reflecting sulfate aerosols, which originate from the rapid industrialization of China. Chinese coal-burning in particular doubled in the 4 years from 2003-2007, and makes up some 77% of the 26% global aerosol increase over that time. Unfortunately, aerosols fall out of the atmosphere fairly quickly, while carbon dioxide remains there for centuries or longer.

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The Atmosphere: What We Know

• Only 2.3% of warming goes into the atmosphere.
• Within one year, from summer to winter, global mean tropospheric temperatures vary by as much as 1.5°C (2.7°F).
• Year to year, from one season to the next, global mean tropospheric temperatures can vary by as much as 1°C (1.8°F).
• Year to year, from one season to the next, global mean surface air temperatures can vary by as much as 0.2°C (0.36°F).
• A minimum of 17 years is needed to accurately detect and confirm a trend — a steady change — in the rise of atmospheric temperatures.
• A variety of natural (temporary) factors combined in the past decade to produce a strong cooling influence on atmospheric temperatures.
• The known anthropogenic warming component has offset and overpowered natural cooling factors, so that a slight warming trend is still detectable.
• Natural cooling factors (a preponderance of La Niña events, weak solar output, increased anthropogenic aerosols) are temporary, while the effects of anthropogenic CO₂ are effectively permanent.

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The Atmosphere: How We Know

Scientists have successfully measured air temperatures around the globe, both at the surface and in the troposphere and stratosphere, in the present as well as in the distant past.

Surface air temperatures have been accurately measured and homogenized — meaning “made comparable” — using scientific instruments and rigorous collection and analysis techniques.

Tropospheric and stratospheric temperatures have been accurately measured using an array of long-lived satellites which measure the radiation, primarily microwaves, emitted by the atmosphere.

Past temperatures have been measured using a variety of different proxies, which have been compared to check their validity and confirm their accuracy. Proxy methods include the measurement of the frequency of stable atmoic isotopes, such as ¹⁷O and ¹⁸O (“heavy hydrogen”), in ice cores and ocean sediments, the evaluation of ancient pollen, flora and fauna in lake and ocean sediments,and other methods.

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The Land

Until 2001, scientists had mostly concentrated on detecting heat uptake by the atmosphere and oceans and by melting ice. That year, however, a group of scientists published a study3 which attempted to measure the heat uptake by the lithosphere — the outermost rocky shell of the earth. That study found that heat absorbed by land actually roughtly matches the amount of heat absorbed by melting ice (such as the Greenland Ice Sheet, polar ice caps, and glaciers). The heat absorbed (only) by land also substantially matches that absorbed to date by the atmosphere.

Thus, the heat uptake by the continents is a tangible and necessary component in computing the total increase in heat in the entire earth system due to anthropogenic warming. This uptake accounts for about 2% of the heat absorbed by the earth's climate system.

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Melting Ice

The earth houses vast amounts of water in the form of (once) permanent ice. This includes ice at the Arctic and Antarctic poles, the Greenland Ice Sheet, and over 130,000 glaciers. Due to global warming, much of this ice is melting at an alarming rate26. That permanent ice melt, in turn, absorbs a lot of heat and produces a vast amount of liquid water. Still, this ice melt only accounts for 2% of the total heat absorbed by the earth's climate.

Glaciers Greenland Arctic Antarctic What We Know How We Know Back

Melting Ice: Glaciers

Glaciers are dynamic, living rivers of ice. They are fed at their source by precipitation which falls as or freezes into ice. Packed and forced to flow by gravity, these rivers slowly and inexorably carve valleys down mountain sides, until the ice reaches an altitude below which temperatures are above freezing, and they melt.

While these glaciers continue to be fed from above — subject to potential changes in precipitation patterns due to climage change — as global temperatures rise, the altitudes at which their ice melts also rise, shortening and in some cases completely eliminating the glacier.

Nearly 1% of all heat absorbed by the earth's changing climate currently goes into shrinking the size of glaciers. More importantly, measurements show that this ice loss is accelerating131415 .

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Melting Ice: Greenland

The Greenland Ice Sheet (GIS) is a unique feature on earth. Greenland is the world's largest island, at 2,166,086 square kilometers (836,109 sq mi). It is home to one of only two permanent ice sheets on earth, most of which is between 2 and 3 kilometers (1 and 2 miles) thick. If the entire ice sheet were to melt it would raise sea levels by 7.2 meters.

The coastal regions have been observed to be losing ice mass while the interior is in approximate mass balance. The overall result is that the Greenland ice sheet is losing ice mass1617. Further evidence suggests that although ice losses have up to this point primarily occurred in the South and Southwest portions of Greenland, these losses are now spreading to the Northwest sector of the ice sheet18. The current rate of loss is over 250 gigatons (billion tons) per year, and that rate has been continuosly accelerating.

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Melting Ice: Arctic

Arctic ice represents one pole (which is very different from the other). The Arctic is an ocean, surrounded by land, at one end of the globe (the North Pole). In that position, for a good portion of the year it receives no sunlight at all, while for an equal portion it receives extended, albeit very indirect, daylight — at times for 24 hours a day.

With this dynamic, the water in the Arctic is able to freeze over completely during the winter. In the summer months, some Arctic ice has always melted, but prior to recent decades, the bulk of the ice remained completely frozen. Since 1979, scientists have been using satellites to track the ice extent, which is erratically but systematically shrinking. Satellite radar altimetry and satellite laser altimetry find that Arctic sea ice has also been thinning1920. The Arctic is expected to have a completely ice free summer sometime this century21. This means that each winter the ice is not re-freezing to the winter extent and volume of the previous year.

Year after year, despite the ongoing fluctuations, the Arctic is losing ice mass.

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Melting Ice: Antarctic

Antarctic ice represents one pole (which is very different from the other). Antarctica is a continent, at one end of the globe (the South Pole). In that position, for a good portion of the year it receives no sunlight at all, while for an equal portion it receives extended, albeit very indirect, daylight — at times for 24 hours a day. Due to the altitude of its mountains it contains masses of ice which have no opportunity to melt, regardless of climate change.

At lower altitudes, the ice is subject to melting. Beyond this, much of the ice in Antarctica rests in the ocean, submerged by its own weight. But as the ocean waters warm, that ice is melting from beneath22. The result of this warming is that Antarctica is losing ice mass23.

Winter Antarctic sea ice extent is increasing, although it melts completely back to the Antarctic coast each summer, so it is of no consequence in the planetary heat budget. Ozone levels over Antarctica have dropped causing stratospheric cooling and increasing winds, which lead to more areas of open water that can be frozen24. In addition, the Southern Ocean is freshening because of increased rain and snowfall as well as an increase in meltwater coming from the edges of Antarctica's land ice25. Fresh water freezes more readily than salt water.

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Melting Ice: What We Know

• Arctic sea ice is thinning and losing mass.
• Summer Arctic sea ice is gradually retreating, and may be completely gone within this century.
• The Antarctic Ice Sheet is losing mass.
• The Greenland Ice Sheet is losing mass.
• The vast majority of the world's glaciers are losing mass.
• Melted ice will add dramatically to sea level rise.
• Less ice means less reflected sunlight, which will add significantly to global warming.
• Melting ice currently accounts for about 2% of the earth's climate system heat uptake.

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Melting Ice: How We Know

Scientists employ a variety of instruments and craft to measure ice mass. In the early 20^th century, such measurements were restricted to visiting and directly observing the outer edges of the Arctic ice pack. Scientists still visit the reaches of the earth, using ever more sophisticated instruments, including floating buoys with arrays of sensors and cameras, to catalog the state of the Cryopshere — the world of snow and ice on earth.

Today, changes in the elevation of large ice sheets are measured with extreme accuracy using both laser and radar altimetry. Sensors based on aircraft or satellites measure the distance from the sensor to the ice surface. By repeating the measurements over time, changes are determined. The twin GRACE satellites, launched by NASA in 2002, use lasers to measure minute changes in the distance between the two craft. These variations in distance in turn reflect variations in mass in the earth below, and so act as a measurement (again, over time) of changes in mass loss of the ice sheets. Other satellites use photography, both visible and infra-red, to catalog the ice extents in the Arctic and the size of glaciers.

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References

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