Climate Change: How Do We Know?

NASA

This graph, based on the comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO₂ has increased since the Industrial Revolution. (Credit: Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record.) Find out more about ice cores (external site).

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 Earth's orbit that change the amount of solar energy our planet receives.

Scientific evidence for warming of the climate system is unequivocal.
- Intergovernmental Panel on Climate Change

The current warming trend is of particular significance because most of it is extremely likely (greater than 95 percent probability) to be the result of human activity since the mid-20^th century and proceeding at a rate that is unprecedented over decades to millennia.¹
Earth-orbiting satellites and other technological advances have enabled scientists to see the big picture, collecting many different types of information about our planet 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.² 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 Earth's climate responds to changes in greenhouse gas levels. Ancient evidence can also be found in tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks. This ancient, or paleoclimate, evidence reveals that current warming is occurring roughly ten times faster than the average rate of ice-age-recovery warming.³

The evidence for rapid climate change is compelling:

Sea level rise Image: Republic of Maldives: Vulnerable to sea level rise Global sea level rose about 8 inches in the last century. The rate in the last two decades, however, is nearly double that of the last century.4 Links Earth's vital signs: Sea Level Quiz: Sea level	Global temperature rise The planet's average surface temperature has risen about 2.0 degrees Fahrenheit (1.1 degrees Celsius) since the late 19th century, a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere.5 Most of the warming occurred in the past 35 years, with 16 of the 17 warmest years on record occurring since 2001. Not only was 2016 the warmest year on record, but eight of the 12 months that make up the year — from January through September, with the exception of June — were the warmest on record for those respective months.6 Links Earth's vital signs: Global temperature Global Climate Change: Causes Graphic: Global warming from 1880 to 2015
Warming oceans 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 1969.7 Links Climate Kids: What is happening in the ocean? Video: Oceans of climate change Article: Warming ocean causing most Antarctic ice shelf mass loss	Shrinking ice sheets Image: Flowing meltwater from the Greenland ice sheet 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. Links Vital Signs: Land Ice Global Ice Viewer
Declining Arctic sea ice Image: Visualization of the 2007 Arctic sea ice minimum Both the extent and thickness of Arctic sea ice has declined rapidly over the last several decades.8 Links Earth's vital signs: Sea ice Interactive: Global ice viewer NASA's Operation Icebridge mission	Glacial retreat Image: The disappearing snowcap of Mount Kilimanjaro, from space. Glaciers are retreating almost everywhere around the world — including in the Alps, Himalayas, Andes, Rockies, Alaska and Africa.9 Link Interactive: Global ice viewer
Extreme events The number of record high temperature events in the United States has been increasing, while the number of record low temperature events has been decreasing, since 1950. The U.S. has also witnessed increasing numbers of intense rainfall events.10 Links Precipitation Measurement Missions Precipitation Quiz	Ocean acidification Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30 percent.11, 12 This increase is the result of humans emitting more carbon dioxide into the atmosphere and hence more being absorbed into the oceans. The amount of carbon dioxide absorbed by the upper layer of the oceans is increasing by about 2 billion tons per year.13, 14 Links How does climate change affect coral reefs The Other Carbon Dioxide Problem
Decreased snow cover Satellite observations reveal that the amount of spring snow cover in the Northern Hemisphere has decreased over the past five decades and that the snow is melting earlier.15 Links National Snow and Ice Data Center Earth Observatory: Snow Cover

References

1. IPCC Fifth Assessment Report, Summary for Policymakers
   B.D. Santer et.al., "A search for human influences on the thermal structure of the atmosphere," Nature vol 382, 4 July 1996, 39-46
   Gabriele C. Hegerl, "Detecting Greenhouse-Gas-Induced Climate Change with an Optimal Fingerprint Method," Journal of Climate, v. 9, October 1996, 2281-2306
   V. Ramaswamy et.al., "Anthropogenic and Natural Influences in the Evolution of Lower Stratospheric Cooling," Science 311 (24 February 2006), 1138-1141
   B.D. Santer et.al., "Contributions of Anthropogenic and Natural Forcing to Recent Tropopause Height Changes," Science vol. 301 (25 July 2003), 479-483.
2. In the 1860s, physicist John Tyndall recognized the Earth's natural greenhouse effect and suggested that slight changes in the atmospheric composition could bring about climatic variations. In 1896, a seminal paper by Swedish scientist Svante Arrhenius first predicted that changes in the levels of carbon dioxide in the atmosphere could substantially alter the surface temperature through the greenhouse effect.
3. National Research Council (NRC), 2006. Surface Temperature Reconstructions For the Last 2,000 Years. National Academy Press, Washington, D.C.
   http://earthobservatory.nasa.gov/Features/GlobalWarming/page3.php
4. https://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf
   Church, J. A. and N.J. White (2006), A 20th century acceleration in global sea level rise, Geophysical Research Letters, 33, L01602, doi:10.1029/2005GL024826.
   The global sea level estimate described in this work can be downloaded from the CSIRO website.
5. https://www.ncdc.noaa.gov/indicators/
   http://www.cru.uea.ac.uk/cru/data/temperature
   http://data.giss.nasa.gov/gistemp
6. https://www.giss.nasa.gov/research/news/20170118/)  
7. Levitus, et al, "Global ocean heat content 1955–2008 in light of recently revealed instrumentation problems," Geophys. Res. Lett. 36, L07608 (2009).
8. L. Polyak, et.al., "History of Sea Ice in the Arctic," in Past Climate Variability and Change in the Arctic and at High Latitudes, U.S. Geological Survey, Climate Change Science Program Synthesis and Assessment Product 1.2, January 2009, chapter 7
   R. Kwok and D. A. Rothrock, "Decline in Arctic sea ice thickness from submarine and ICESAT records: 1958-2008," Geophysical Research Letters, v. 36, paper no. L15501, 2009
   http://nsidc.org/sotc/sea_ice.html
9. National Snow and Ice Data Center
   World Glacier Monitoring Service
10. "Attribution of Extreme Weather Events in the Context of Climate Change," National Academies Press, 2016
    https://www.nap.edu/read/21852/chapter/1
    Kunkel, K. et al, "Probable maximum precipitation and climate change," Geophysical Research Letters, (12 April 2013) DOI: 10.1002/grl.50334
    Kunkel, K. et al, "Monitoring and Understanding Trends in Extreme Storms: State of the Knowledge," Bulletin of the American Meteorological Society, 2012.
    http://lwf.ncdc.noaa.gov/extremes/cei.html
11. http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F
12. http://www.pmel.noaa.gov/co2/story/Ocean+Acidification
13. C. L. Sabine et.al., "The Oceanic Sink for Anthropogenic CO2," Science vol. 305 (16 July 2004), 367-371
14. Copenhagen Diagnosis, p. 36.
15. National Snow and Ice Data Center
    C. Derksen and R. Brown, "Spring snow cover extent reductions in the 2008-2012 period exceeding climate model projections," GRL, 39:L19504
    http://nsidc.org/cryosphere/sotc/snow_extent.html
    Rutgers University Global Snow Lab, Data History Accessed August 29, 2011.

Adani Is Not Just Another Coalmine, It Is A Turning Point For The Nation

The Guardian - Hamish McKenzie

If the government approves this monstrous mine it will be committing environmental treason against every Australian who values our farmers, our coasts, our bush and our way of life

Protesters in Canberra hold banners and signs during a 12 April demonstration against Indian company Adani Enterprises building one of the world’s biggest coal mines in Australia. Photograph: Reuters

In an almost unbroken line from Monkey Mia, down across the Bight and then all the way up the other side to Mackay, the Australian coast is etched in various shades of brown. This is the historical precipitation map. Annual rainfall has dropped, it shows, across this enormous stretch of coastline, by as much as 100 millilitres since 1951.
In another map, concentric rings of increasingly angry red emanate from the centre of the continent. This one shows that, assuming we keep going as we are, the temperature in our country will increase by as much as 5C by the end of the century. Eight, if we’re unlucky.
This, by the way, is not the marketing material of some lefty environmental organisation. This is the product of thousands of the world’s top climate scientists, using some of the most sophisticated computer models ever built, to generate projections so fine-grained they simulate even the amount of moisture in every parcel of soil on the planet, and in the poles, the thickness of every chunk of sea ice.
These models give a glimpse of the Australia we are creating. They show the nation’s wheatbelts, from Esperance to the Wimmera, dried to a crisp. They show the Queensland coast being thrashed more relentlessly by fiercer storms. They show a rash of summer bushfires that make Black Saturday look like candles on a cake. But they do not show the reef. By the end of the century, we will have boiled it to death.
This is the Australia we are creating. Even more, it is the Australia we will have to accept if the Adani mine is approved.
Research published last year by four Oxford economists and scientists concluded that to keep climate change to below 2C, no new coal plants can be built after 2017 unless they have zero emissions. That means perfectly efficient carbon capture and storage would have to be deployed on every coal plant in the world – an absurd fantasy.

The paper also finds we already have in place sufficient “capital stock” – the global network of mines and electricity generators – to push us over 2C. At the same time, global coal demand has already peaked and is now falling, China and India have frozen construction on over 100 coal plants, and the economics of energy are pointing only in one direction: renewables.
This points to a stark lose-lose equation for potential new mines like Adani’s: either we burn their coal and induce dangerous climate change, or we don’t and waste billions of dollars.
Unless, of course, we take the third option: don’t build the thing. This is not, then, just another coalmine. It is a turning point. If we build Adani, we commit to irreparably harming Australia’s precious environment. If we don’t, we might still have a chance to save it. This is where we as a nation decide if we will be Asia’s rockpit for another 50 years, or a prosperous nation for the next 500.
Research just released shows that to avoid dangerous climate change, we need anthropogenic emissions to halve every decade. Building the biggest coalmine in history, when there is already a global glut and sufficient investment to tip us over the edge, is not what responsible conservative governments should be doing. They should be conserving all that is precious to us. Serving us. Instead, they are preparing to betray us.
If the world in 2077 is still burning as much coal as we are today, and the financial model of the Adani assumes it will, Australia as we know it – our wheatbelts, our reefs, our cities, and our lifestyles – will cease to exist.
Our government, sworn to protect the nation, should be doing everything it can to avert this looming crisis, not be falling over themselves to pay for the executioner’s bullet. If the government approves this monstrous mine, and the banks fund it, it will be committing environmental treason against every Australian who values our farmers, our coasts, our bush, and our way of life. We are about to choose Adani or Australia.
The argument against Adani achieves that rare distinction of finding purchase among all parts of society: patriots and cosmopolitans, environmentalists and economists, parochialists and internationalists, the job-hungry regions and the growth-hungry cities. We must all stop this affront to our nation. We must choose Australia.

Links

• The Adani mine is this generation's Franklin River. People power can stop it
• It’s either Adani or the Great Barrier Reef. Are we willing to fight for a wonder of the world?
• Footage shows wetlands blackened by Abbot Point coal dust, activists say
• Adani mine must stand on its own two feet, Labor's Jason Clare says
• Loss of coral reefs caused by rising sea temperatures could cost $1tn globally
• Malcolm Turnbull tells Indian billionaire native title will not stop Adani coalmine
• Coalition backbencher breaks ranks with colleagues over $1bn Adani rail loan
• Adani mine needs $1bn public funding to go ahead, Barnaby Joyce says
• It's either Adani or the Great Barrier Reef. Are we willing to fight for a wonder of the world?
• Don't fund coal mine, activists plead with Australian export credit agency
• Adani mine railway loan would breach government's policy, says legal group
• 'Irreversible consequences': Adani coalmine granted unlimited water access for 60 years
• The Adani mine is this generation's Franklin River. People power can stop it
• Labor to support native title changes to protect mining deals
• Ian and Greg Chappell call on Adani to abandon Carmichael mine project
• Stopping global warming is only way to save Great Barrier Reef, scientists warn

How High Will Global Sea Levels Rise?

Cosmos - James Mitchell Crow

Predicting the rate of Antarctica's ice melt is tricky business as the rise in global sea levels depends on the state of the ice cap. New research suggests it may be worse than we thought, writes James Mitchell Crow.

In the low-lying Netherlands, floating houses such as these in Ijberg, a suburb of Amsterdam, are ready for higher sea levels. Whether housing in other places should be built this way depends largely on what happens with Antarctica. Ashley Cooper / Getty Images

Estimates of global sea level rise by 2100 have fluctuated wildly in recent decades – from more than two metres to as little as 31 centimetres.
The rubbery figures have been a source of ammunition for climate change sceptics and consternation for policy makers – undermining their ability to plan ahead. Most of the blame can be levelled at Antarctica. Its 30 million km3 ice sheet holds 90 per cent of the world's fresh water. If it all melted, sea levels would rise 60 metres. By contrast, a melt of the Greenland ice sheet, the world's second largest, would contribute six metres.
Predicting the rate of ice melt in Greenland is relatively straightforward; Antarctica's melt is anything but.
The stability of Antarctica's ice sheet depends on the floating ice shelves at its fringes. They act as plugs halting the movement of the ice sheet. It is the dynamics of that interaction that have been hard to fathom.
The most recent IPCC report (published in 2013) estimated Antarctic ice would contribute just 4 centimetres to global sea levels by the end of the century, leading to an overall rise of 70 centimetres by the end of the century under "business as usual" emissions scenarios.
That estimate, according to Nick Golledge, an Antarctic ice sheet modeller at Victoria University of Wellington, in New Zealand, was extremely conservative, because the report's authors "just didn't know enough about fast dynamics in ice sheets". Scientific understanding has moved on since then, confirming Antarctica will contribute way more than 4 centimetres by 2100. "The latest research is converging on a figure more like half a metre," Golledge says.
Researchers discovered how unpredictable ice sheet dynamics could be in 2002 when a 3,500 km2 chunk of the Larsen B ice shelf disintegrated. Located on the Antarctic Peninsula, the continent's most northerly and warmest point, it had appeared perfectly stable.
While the melting of Larsen B didn't make any direct difference to sea levels (just as the melting of an ice block won't raise the level of your drink), it was the canary in the coal mine.
Before the Larsen B event, scientists thought the ice sheet moved in a very steady fashion, says Matt King, who researches Antarctica's contribution to sea level rise at the University of Tasmania. "You could kick it as much as you like and it didn't really do much... Now we have a completely different view."
What led to the collapse of Larson B was the rising summer temperatures in the Antarctic peninsula, with the mercury spending more and more time above zero in the years beforehand. As a result, vast pools of meltwater formed on top of the thinning ice, fracturing it and pouring into cracks that ultimately broke apart the whole chunk.
Summer surface melting is a well-understood process, and the dominant factor in Greenland's melt – making it highly predictable. The process can explain what is happening in the northern tip of Antarctica, but it can't account for the changes seen in the rest of the southern continent, where temperatures perpetually remain well below freezing. Here the peril seems to come from below.
One "hotspot" in East Antarctica is the rapidly thinning ice shelf fringing the large Totten glacier. In a study published in Science Advances in December 2016, a CSIRO-led team confirmed warm water from the deep ocean is slipping up onto the Antarctic continental shelf and reaching Totten via deep canyons in the sea floor.

As the ice warms, thins and cracks, yet another feedback mechanism might come into play, according to modelling.

"If there's one thing ice hates, it's warm water – it's tremendously efficient at melting ice," King says.
That warm water is not just a threat to the floating ice shelves. In West Antarctica the ice sheet sits on bedrock that is below sea-level, raising the risk warmer water could stream in and undercut the ice sheet.

Slip sliding away: Antarctica on the move. Cosmos DATA SOURCE: DeConto & Pollard, Nature, 2016.

As the ice warms, thins and cracks, yet another feedback mechanism might come into play, according to modelling by Robert DeConto at the University of Massachusetts and David Pollard at Pennsylvania State University. Each time a piece of ice shelf breaks off, the remaining "ice cliffs" will be taller. "That's inherently unstable," says Tony Worby, who heads the Antarctic Climate and Ecosystems Cooperative Research Centre in Hobart. Sooner or later the cliffs will crumble under their own weight.
Understanding these processes is just the beginning of the ice modellers' work. Predicting when, where and how rapidly they will occur, to forecast how much sea levels will rise, is quite another. So far the estimates of Antarctic contribution to sea level rise by 2100 remain highly variable. A key challenge is the lack of data to feed into the models. Huge sections of East Antarctica's coastal zone remain effectively unmapped. "We don't know where the bedrock is or where the warm water can flow," King says.
In 2019, Australian researchers will take delivery of a new icebreaker able to map the seafloor on Antarctica's fringe. The ship will carry an unmanned underwater vehicle capable of navigating under the ice shelves. "Very quickly we'll start to build a picture of what the seafloor looks like around the continental shelf around Antarctica," King says.
Within a decade, researchers should be more confident in their predictions. "Assuming," King notes, "there's not more unknown aspects of the ice sheet." We've been surprised before.

Links

• What happens if the permafrost disappears?
• How much ice can Antarctica afford to lose?
• Most sea-level rise since 1970 due to greenhouse gas emissions
• Short-term greenhouse gases cause long-term sea level rise
• Global warming levels masked by aerosols: study