Friday, 25 May 2018

Climate Change - How Ice Ages come & go, & why things are different now



Some people claim the current climate change has "natural causes".

They talk about the changes during the 'Ice Age', thinking the current events must be natural as well.

Scientists say that is not the case.

The current situation is different.

The things that caused the changes in the Ice Age are not exactly the same this time.

The graph below shows that carbon dioxide in the air has increased and decreased over hundreds of  thousands of years.

The recent increase in carbon dioxide is much bigger and faster than the natural changes.



The low readings match with times called 'glacial stages'.

During glacial stages, ice covered large areas of the Earth.


The most recent glacial stage occurred between 115,000 and 11,500 years ago. 


Glacial stages begin when those cycles cause cooling.

Glacial stages end when those cycles cause warming.

These cycles change how much solar energy reaches the Earth.

This warming changes the amount of carbon dioxide that can dissolve in the oceans.

So in that early phase, the temperature rises first, before the CO2 level rises.

(This is why some people say "CO2 lags behind temperature rise" ... which is only true in this special situation).


Then as the Earth warms, more carbon dioxide leaves the oceans.

The extra carbon dioxide gas in the air then boosts the warming effect.

At present, Milankovitch Cycles are trying to cool the Earth.

So the current warming is not part of natural processes.



Law Dome is a site in Antarctica where scientists have drilled into the ice.

Global temperatures are responding to the recent big increase in carbon dioxide.

The extra carbon dioxide has come mainly from burning fossil fuels.

The rise in carbon dioxide now means the cycle of glacial and interglacial stages may have been broken.

A research paper has looked at that issue:

"...the end of the current interglacial would occur within the next 1500 years, if atmospheric CO2 concentrations did not exceed 240±5ppmv."

So carbon dioxide would need to drop a long way below the current level for this interglacial to end.

Thursday, 24 May 2018

Climate Change - Rising sea level linked to warmer seas, and melting ice

Sea level is rising, and there are several reasons connected to global warming.


An international team of researchers has produced this graph of ocean levels, for a period of time going back to around 500 BC. 

Extra water enters the sea when ice melts from Antarctica, Greenland and other glaciers and ice caps.

Recent research suggests that the glaciers of Alaska alone now contribute 75 gigatonnes per year.

Seawater also expands as it gets warmer, just like the liquid in a thermometer expanding as temperatures rise.  This is called 'thermal expansion.'



Investigating sea level rise involves scientists using many different methods, including satellites which map the surface of the sea.

It is also important to look carefully at older records from tidal gauges all over the world.

Global sea level rise from the 20th century to the last two decades has speeded up even more than scientists previously thought, according to a new Harvard study.

NASA have reported a global sea rise of 6 cm in the last 2 decades. 

For an idea of how sea level rise might affect you: SEA LEVEL MAPS

Wednesday, 23 May 2018

Climate Change - Early steps in Climate Science


1800-1870 

Level of carbon dioxide gas (CO2) in the atmosphere, as later measured in ancient ice, was about 290 ppm (parts per million).



Global temperature for 1850-1870 was about 13.6°C.

1824
Jean-Baptiste Joseph Fourier calculated that the Earth would be far colder if it lacked an atmosphere. 



1856

Eunice Foote describes filling glass jars with water vapour, carbon dioxide and air, and comparing how much they heated up in the sun.
“The highest effect of the sun’s rays I have found to be in carbonic acid gas,” 
 “The receiver containing the gas became itself much heated – very sensibly more so than the other – and on being removed, it was many times as long in cooling.”
1859
John Tyndall discovered that some gases block infra-red radiation. 



He suggested that changes in the concentration of the gases could bring climate change.





1930s 
Milutin Milankovitch proposed orbital changes as the cause of ice ages. 

1938 
Guy Callendar showed that global warming was underway, reviving interest in the question. 


1950s 
By accident, Russell Coope discovered that some past climate change events happened in just a few decades.



This came from his research into beetle fossils in 'Ice Age' layers.

1958 
Telescope studies showed a greenhouse effect raises temperature of the atmosphere of Venus far above the boiling point of water. 



1960 

Charles David Keeling accurately measured CO2 in the Earth's atmosphere.

He was not expecting to detect an annual rise.

The CO2 level was 315 parts per million (ppm)and global temperature (five-year average) was 13.9°C.

Keeling's measurements have been continued.



By the end of 2015 the level was over 400 ppm.

Global temperature in 2015 was 14.80°C.

Tuesday, 22 May 2018

Climate Change - The last 1,000 years of global temperatures

Average global temperature is now higher than it has been for a long time.


Graph by Klaus Bitterman.

Green dots show the 30-year average of the PAGES 2k reconstruction. 

The red curve shows the global mean temperature, based on HadCRUT4 data from 1850 onwards. 

In blue is the original "hockey stick" from paper by Mann, Bradley and Hughes (1999) with its uncertainty range (light blue). 

The green dots are calculated using data from many places around the world, using information from a range of temperature proxies, such as documents, ice, lakes, pollen, tree rings, corals, seabeds and speleothems.
78 researchers from 24 countries, together with many other colleagues, worked for seven years in the "PAGES 2k" Project on this climate reconstruction. 

Their study is based on 511 climate archives from around the world.

PAGES is the Past Global Changes programme launched in 1991. 

Monday, 21 May 2018

Climate Change - Evidence from Ice Cores

Ice cores are cylinders of ice, drilled from an ice sheet or a glacier. 


They are usually 10 centimetres in diameter, and can be taken from deep in the ice.

Ice cores provide trapped samples of ancient air.


"Air bubbles trapped in ice are like little time capsules that record the past atmospheric composition. 

"So we measure loads of different gases, and essentially we can measure greenhouse gases such as carbon dioxide and methane."

Most ice core records come from Antarctica and Greenland.


Law Dome is a location in Antarctica.

The evidence in Law Dome ice cores shows that since the 18th century, when the Industrial Revolution began, the level of carbon dioxide has risen.

Now it has reached around 400 ppm, a rise of 85 ppm in just 56 years.  

The longest ice cores are from 3km deep in ice. 

The oldest ice core records extend 123,000 years in Greenland, and now to 1 million years in Antarctica. 


The graph shows how carbon dioxide has increased and decreased over hundreds of  thousands of years.

During glacial stages, ice covered large areas of the Earth.

The most recent glacial stage occurred between about 120,000 and 11,500 years ago. 



Since then, the Earth has been in an interglacial period called the Holocene.

During glacial stages, CO2 levels were around 200 parts per million (ppm).

During the warmer interglacial periods, they hovered around 280 ppm. 

In 2013, CO2 levels passed 400 ppm for the first time in recorded history. 

A new study using evidence from a highly detailed ice core from West Antarctica shows a link between abrupt temperature changes on Greenland and Antarctica during the last ice age.

Sunday, 20 May 2018

Climate Change - Repeat photography of melting glaciers

Glaciers are melting quickly in many places.

Grinnel Glacier- at the top, 1940, compared with the lower image from 2006. Repeat photography reveals this process.

Embedded image permalink

Mount Lyell is in Yosemite National Park, California.

New research shows that glacier retreat is a global phenomenon and is being caused by climate change:
....in many places, the centennial-scale retreat of the local glaciers does indeed constitute categorical evidence of climate change.
In 2014Exit Glacier in Alaska melted and retreated 57 metres toward the Harding ice field, which itself has lost 10 per cent of its mass since 1950.


Saturday, 19 May 2018

Climate Change - The Iceman

In places which are not as frozen as they were, amazing discoveries have been made.


In 1991 two hikers in the Alps found a body.

They were shocked, and reported the find.

It was even more extraordinary when the investigation found that the body was thousands of years old.



The clothing, weapons and other items found with the body give a glimpse into life when metal was first being used.



Tests later confirmed the iceman dates back to 3,300 BC.

He probably died from a blow to the back of the head. 


His body was so well-preserved that scientists were able to determine that his last meal was red deer, herb bread, wheat bran, roots and fruit.


He lived at a time, over 5,000 years ago, when the Earth was starting to cool.



So when he died high in the mountains, his body became covered with snow.

Modern warming (shown by the red part of the graph) made it possible to find him.