Burning fossil fuels is responsible for most sea-level rise since 1970


Aimée Slangen, Utrecht University and John Church, CSIRO

Global average sea level has risen by about 17 cm between 1900 and 2005. This is a much faster rate than in the previous 3,000 years.

The sea level changes for several reasons, including rising temperatures as fossil fuel burning increases the amount of greenhouse gases in the atmosphere. In a warming climate, the seas are expected to rise at faster rates, increasing the risk of flooding along our coasts. But until now we didn’t know what fraction of the rise was the result of human activities.

In research published in Nature Climate Change, we show for the first time that the burning of fossil fuels is responsible for the majority of sea level rise since the late 20th century.

As the amount of greenhouse gases we are putting into the atmosphere continues to increase, we need to understand how sea level responds. This knowledge can be used to help predict future sea level changes.


CSIRO

Measuring sea level

Nowadays, we can measure the sea surface height using satellites, so we have an accurate idea of how the sea level is changing, both regionally and in the global mean.

Prior to this (before 1993), sea level was measured by tide gauges, which are spread unevenly across the world. As a result, we have a poorer knowledge of how sea level has changed in the past, particularly before 1960 when there were fewer gauges.

Nevertheless, the tide gauge measurements indicate that global mean sea level has increased by about 17 cm between 1900 and 2005.

What drives sea level rise?

The two largest contributors to rising seas are the expansion of the oceans as temperatures rise, loss of mass from glaciers and ice sheets, and other sources of water on land. Although we now know what the most important contributions to sea-level rise are, we did not know what is driving these changes.

Changes in sea level are driven by natural factors such as natural climate variability (for example El Niño), ongoing response to past climate change (regional warming after the Little Ice Age), volcanic eruptions, and changes in the sun’s activity.

Volcanic eruptions and changes in the sun affect sea level across years to decades. Large volcanic eruptions can cause a temporary sea-level fall because the volcanic ash reduces the amount of solar radiation reaching the ocean, thus cooling the ocean.

Humans have also contributed to sea level rise by burning fossil fuels and increasing the concentration of greenhouse gases in the atmosphere.

Separating the causes

We used climate models to estimate ocean expansion and loss of mass from glaciers and ice sheets for each of the individual factors responsible for sea level change (human and natural). To this we added best estimates of all other known contributions to sea level change, such as groundwater extraction and additional ice sheet contributions.

We then compared these model results to the observed global mean 20th century sea-level change to figure out which factor was responsible for a particular amount of sea level change.

Over the 20th century as a whole, the impact of natural influences is small and explains very little of the observed sea-level trend.

The delayed response of the glaciers and ice sheets to the warmer temperatures after the Little Ice Age (1300-1870 AD) caused a sea-level rise in the early 20th century. This explains much of the observed sea-level change before 1950 (almost 70%), but very little after 1970 (less than 10%).

The human factor

The largest contributions to sea-level rise after 1970 are from ocean thermal expansion and the loss of mass from glaciers in response to the warming from increasing greenhouse gas concentrations. This rise is partly offset by the impact of aerosols, which on their own would cause a cooling of the ocean and less melting of glaciers.

The combined influence of these two factors (greenhouse gases and aerosols) is small in the beginning of the century, explaining only about 15% of the observed rise. However, after 1970, we find that the majority of the observed sea-level rise is a direct response to human influence (nearly 70%), with a slightly increasing percentage up to the present day.

When all factors are considered, the models explain about three quarters of the observed rise since 1900 and almost all of the rise over recent decades (almost 90% since 1970).

The reason for this difference can be found either in the models or in the observations. The models could underestimate the observed rise before 1970 due to, for instance, an underestimated ice sheet contribution. However, the quality and number of sea level observations before the satellite altimeter record is also less.

Tipping the scales

Our paper shows that the driving factors of sea-level change have shifted over the course of the 20th century.

Past natural variations in climate were the dominant factor at the start of the century, as a result of glaciers and ice sheets taking decades to centuries to adapt to climate change.

In contrast, by the end of the 20th century, human influence has become the dominant driving factor for sea-level rise. This will probably continue until greenhouse gas emissions are reduced and ocean temperatures, glaciers and ice sheets are in equilibrium with climate again.


John will be on hand for an Author Q&A between 4 and 5pm AEST on Tuesday, April 12, 2016. Post your questions in the comments section below.

The Conversation

Aimée Slangen, Postdoctoral research fellow, Institute for Marine and Atmospheric Research, Utrecht University and John Church, CSIRO Fellow, CSIRO

This article was originally published on The Conversation. Read the original article.

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97 out of 100 climate scientists agree: Humans are responsible for warming


Grist

The Earth revolves around the sun. Also, it’s overheating because we’re burning fossil fuels.

Can you guess which of those two long-established facts just received an additional jolt of publicized near unanimity among scientists?

It was, of course, the latter. (The oil industry has no economic interest in attempting to debunk the former, and you can no longer be persecuted for claiming it.)

An international team of scientists analyzed the abstracts of 11,944 peer-reviewed papers published between 1991 and 2011 dealing with climate change and global warming. That’s right — we’re talking about 20 years of papers, many published long before Superstorm Sandy, last year’s epic Greenland melt, or Australia’s “angry summer.”

About two-thirds of the authors of those studies refrained from stating in their abstracts whether human activity was responsible for climate change. But in those papers where a position on the claim was staked out, 97.1 percent endorsed…

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Malcolm Naden: Barrington Tops Warning for Travellers


Travellers to the Barrington Tops are being warned that outlaw and modern bushranger Malcolm Naden is suspected of hiding out in the remote wilderness area. There is currently a $50 000 reward for information that leads to his capture. He is the most wanted person in New South Wales, suspected of being involved in the disappearance of his cousin Lateesha Nolan and the murder of Kristy Scholes in 2005 at Dubbo.

Naden has sought refuge in the bush in the region bordered by Dubbo in the west and Kempsey in the east since 2005. During this time he has broken into homes, stealing non-perishable food items, camping gear and other equipment required to survive the bushland in which he hides and lives. He is known to be an expert bushman.

Naden first hid in the Western Plains Zoo at Dubbo and has since been known to have been in the vicinity of the Barrington Tops. In 2008 he was known to be in the vicinity of Stewarts Brook, in the western Barrington Tops area. In January 2009 he was known to be at Bellbrook, west of Kempsey. Three months ago he was known to be at Mount Mooney, in the northern Barrington Tops. It is thought that he is also responsible for similar break-ins around the Mount Mooney area in late August 2010. There have been a large number of break-ins across the region this year. He is believed to be armed, with a rifle having been stolen in one of the break-ins. Not all of the break-ins are confirmed as being committed by Malcolm Naden, but they all seem to bear his signature.

According to local newspapers, it is also believed that kangaroo carcasses have been found in the Barrington Tops, butchered in an expert manner. Naden was an abattoir worker and similar carcasses were found at the Dubbo zoo when Naden was hiding there.

The area in which Malcolm Naden is thought to be hiding was once the hideout for the bushranger known as ‘Captain Thunderbolt.’ Naden seems to be following in Thunderbolt’s footsteps in more ways than one.

For more on Malcolm Naden visit:

http://www.police.nsw.gov.au/can_you_help_us/wanted/malcolm_john_naden

http://coastmick21.blogspot.com/

http://www.smh.com.au/news/national/police-seek-man-on-run-after-cousin-found-dead/2005/08/21/1124562750384.html

http://www.australianmissingpersonsregister.com/Naden.htm

http://www.brisbanetimes.com.au/news/national/wanted-man-and-a-town-in-fear/2009/01/17/1232213416486.html

http://www.facebook.com/topic.php?uid=4884239637&topic=7725

http://www.theherald.com.au/news/local/news/general/danger-at-the-tops-break-ins-point-to-fugitive/1928579.aspx

http://www.smh.com.au/nsw/publics-help-sought-over-murder-cases-20100904-14v5u.html

Earth Day: April 22


Earth Day is about the earth and the people who live on it. The Earth Day Network believes that all people, no matter who they are, have a right to a healthy and sustainable environment. Those who support Earth Day are a veritable who’s who of environmentalism. The network not only educates and increases awareness of environmental issues, it also actively seeks to bring about change in order to achieve a healthy and sustainable environment.

Earth Day is celebrated on the 22nd April each year, with supporters getting involved in all manner of environmentally responsible activities.

Find out more about Earth Day and the Earth Day Network at:

http://www.earthday.org/

TRAPPED CROCODILE NOT KILLER: Cooktown


The first crocodile trapped in the hunt for a crocodile that may be responsible for the disappearance of Arthur Booker in the Endeavour River near Cooktown in Queensland was not responsible for his disappearance.

The crocodile has now been set free and tests will now be carried out a further two crocodiles that have been caught.

CROCODILE ATTACK: TRAPPING BEGINS NEAR COOKTOWN


The body of Vietnam veteran Arthur Booker, of Logan, Queensland, has still not been found following a suspected crocodile attack earlier this week. It is thought that Booker was taken by a large crocodile while checking crab traps along the Endeavour River near Cooktown on Tuesday. All that has been found in the search for the missing 62-year-old man has been his footwear and watch.

The search for Booker has now entered a new stage with police suspending their search of the river. Queensland Environmental Protection Officers (EPA) have now begun to lay crocodile traps in the area so that crocodiles can be examined for remains without harming or killing them.

The investigation into the disappearance of Arthur Booker has yet to determine if he was in fact taken by a crocodile, although this remains the most likely scenario.  There are a number of large crocodiles inhabiting the area, including the 6m ‘Charlie.’

Charlie is known to be responsible for the loss of pet dogs, livestock, eating a 3.5m crocodile and was once seen taking a horse.

The probable crocodile attack has once again brought the call for crocodile culling back into the public arena. At the moment any thought of culling by officials has been dismissed.

BELOW: Footage reporting the disappearance of Arthur Booker