Wednesday, 31 October 2018

Climate Change - Have humans caused climate change for longer than thought?

An international research project has found human activity has been causing global warming for almost two centuries, according to a report in Phys.Org
Humans have caused climate change for 180 years
Australian National University researcher Associate Professor Nerilie Abram. Credit: Stuart Hay, ANU
Lead researcher Associate Professor Nerilie Abram from The Australian National University (ANU) said that their study found that warming began during the early stages of the Industrial Revolution.

Warming is first detectable in the Arctic and tropical oceans around the 1830s, much earlier than scientists had expected.
CO2 information from ice cores shows that atmospheric CO2 levels began to rise from around 280 ppm as the 19th century began.
Atmospheric CO2 concentration over the last millennium, as reconstructed from ice core data obtained by Etheridge et al. (1998) at Law Dome, Antarctica.

Tuesday, 30 October 2018

Climate Change - The 8,200 year event

When the last glacial period ended about 11,500 years ago, the Earth's modern climate began to develop. 

The large continental ice sheets shrank, and sea level rose.


Around 8,200 years ago, however, a major cooling event occurred. 

The 8.2 ka event was first discovered in the Greenland ice core GISP2.

Over two decades temperature cooled about 3.3°C in Greenland.

Temperatures in Europe dropped by around 2°C.

The entire event lasted about 150 years.

Then temperatures warmed, returning to their previous levels. 

So what caused the 8.2 ka event?

As the large ice sheets in Canada were melting, a large meltwater lake formed south of the Hudson Bay. 

Geologists have named this Lake Agassiz, after the 19th century scientist Louis Agassiz.


It was dammed to the north by the Laurentide ice sheet.

Slowly, the ice melted further, and the lake emptied into the sea in a very short period of time.




The cold water flooding into the Atlantic caused cooling, and the rising sea level formed the North Sea and the English Channel, creating the familiar shape of Britain.

This event shows that the climate can react strongly to sudden changes.

Monday, 29 October 2018

Climate Change - The Atmosphere




Space is not very far away.

Aircraft on long-haul flights travel at a height of about 10 km.

The lowest layer of the atmosphere, the Troposphere, ends at about 15 km.

The air in the layers above the troposphere is very thin indeed.

Think of a place around 15 km (9 miles) from where you are.

That's pretty much how near you are to space.

All the waste gases people dump into the air are trapped in the thin layer of air around the Earth.


Molecules in the air include nitrogen and oxygen as well as water, carbon dioxide, ozone, and many other compounds in trace amounts, some created naturally, others the result of human activity.

In addition to gases, the atmosphere contains extras such as smoke, dust, acid droplets, and pollen.
Atmospheric concentrations of some greenhouse gases over the last 2,000 years. 


The stratosphere starts just above the troposphere and extends to 50 kilometres (31 miles) high. The ozone layer, which absorbs and scatters the solar ultraviolet radiation, is in this layer.


Mesosphere

The mesosphere starts just above the stratosphere and extends to 85 kilometres (53 miles) high. Meteors burn up in this layer

Thermosphere
The thermosphere starts just above the mesosphere and extends to 600 kilometres (372 miles) high. Aurora and satellites occur in this layer.

Ionosphere
The ionosphere is an abundant layer of electrons and ionized atoms and molecules that stretches from about 48 kilometres (30 miles) above the surface to the edge of space at about 965 km (600 mi), overlapping into the mesosphere and thermosphere. This dynamic region grows and shrinks based on solar conditions and divides further into the sub-regions: D, E and F; based on what wavelength of solar radiation is absorbed. The ionosphere is a critical link in the chain of Sun-Earth interactions. This region is what makes radio communications possible.

Exosphere
This is the upper limit of our atmosphere. It extends from the top of the thermosphere up to 10,000 km (6,200 mi).

Sunday, 28 October 2018

Climate Change - Can climate change increase earthquakes and volcanic eruptions?

Between about 20,000 and 5,000 years ago, Earth slowly changed from the frigid conditions of an Ice Age, to the world on which our civilization has developed.

As the ice sheets melted, colossal volumes of water flowed back into the oceans.



The pressures acting on the Earth's crust changed as a result. 

The weight of ice on the continents was reduced, and the rising seas put extra water pressure on the seafloors.

In response, the crust moved up and bent, creating extra volcanic activity, increased seismic shocks and giant landslides.



So if we continue to allow greenhouse gas emissions to rise unchecked, causing serious warming, will our planet's crust react once again?

In Alaska, climate change has pushed temperatures up by more than 3 degrees Celsius in the last half century, and glaciers are melting at a staggering rate, some losing up to 1 kilometre in thickness in the last 100 years. 


The reduced weight on the crust beneath is allowing faults to slide more easily, promoting increased earthquake activity in recent decades. 

The crust beneath the Greenland ice sheet is already rebounding in response to rapid melting, providing the potential for future earthquakes, as faults beneath the ice are relieved of their confining load. 



The possibility exists that these could trigger submarine landslides, making tsunamis capable of threatening North Atlantic coastlines. 

Eastern Iceland is bouncing back as its Vatnaj√∂kull ice cap melts. Research predicts a response from the volcanoes beneath. 

A rise in landslide activity will happen in the Andes, Himalayas, European Alps, and elsewhere, as the ice and permafrost that covers many mountain slopes melts away. 

As sea levels rise, the bending of the crust around the margins of the oceans might unlock coastal faults such as California's San Andreas, allowing them to move more easily.

At the same time, the extra weight of seawater could act to squeeze magma out of undersea volcanoes.



This post is based on the work of Bill McGuire, professor of geophysical and climate hazards at University College London.

Saturday, 27 October 2018

Climate Change - Tropical storms

Hurricanes, cyclones, and typhoons are all the same weather phenomenon.

We use those different names for these tropical storms in different places. 

In the Atlantic and North-East Pacific, the term “hurricane” is used.

Embedded image permalink
Image of Hurricane Patricia tweeted by astronaut Scott Kelly.

In the North-West Pacific a tropical storm is called a “typhoon”, and “cyclones” occur in the South Pacific and Indian Ocean.

Three strong tropical storms (KiloIgnacio, and Jimena), formed in the Pacific in 2015. 

On Sunday 30th August, all of them were a category 4. This was the first time the north-eastern Pacific had seen three category 4 hurricanes at the same time.

Picture hurricanes in Pacific Ocean



Tropical storms can’t form outside the tropics - water temperatures are too cold.

Sea surface temperature must be at least 27°C, and this temperature is actually required to a depth of at least 50 m

The warm tropical atmosphere heats up the water at the ocean surface and begins to evaporate it. 

The trapped water vapour in the air rises up through the atmosphere. 



When the rising air cools, and the water vapour condenses into liquid water, the heat is released back into the atmosphere.

The warm air rushes upward, because it has a lower density than its surroundings. 

This then draws air up from below, and speeds up the rising air near the surface. 

Surface air around the growing disturbance rushes in to replace it. 


A satellite image from the National Oceanographic and Atmospheric Administration shows Hurricane Katrina bearing down on the Gulf Coast on Aug. 28, 2005.

As this cycle continues, more warm, moist air is drawn into the developing storm, and more heat is transferred from the surface of the ocean to the atmosphere. 

This continuing heat exchange creates a wind pattern that spirals around a relatively calm centre, or eye, like water swirling down a drain.

The US National Hurricane Center gives regular information about hurricanes.

Friday, 26 October 2018

Climate Change - Oceans Are Losing Oxygen



Marlin can hunt in water a half mile down, and sailfish often dive deep too.

In more and more places around the world, ocean predators are sticking near the surface.

Why?

Warming temperatures are sucking oxygen out of waters even far out at sea, making enormous stretches of deep ocean hostile to marine life.

New research shows that this problem is getting worse.



Vast stretches of the ocean interior suddenly lost oxygen during the transition out of the last glacial stage, between 17,000 and 10,000 years ago. 

This event was the most recent example of large-scale global warming.

There are other examples in the geological record, including the Zechstein Sea.

Thursday, 25 October 2018

Climate Change - The Last Interglacial

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


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

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

The peaks in the graph show times when carbon dioxide was high, matching times called 'interglacial stages'.

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

The last interglacial period occurred before it, from around 130,000 to 115,000 years ago.

It's official international name is the Eemian, but it has other names in specific places.
Climate information from that time is particularly useful.
During that time, temperatures on earth were higher at the poles than they are now. 
The sea level was between five and nine metres higher than current levels, because of the melting of ice in Greenland and Antarctica.
In the UK, this last interglacial period is called the 'Ipswichian'.
Pleistocene, Ipswichian raised beach deposits at Hope's Nose, Torquay, Devon, seen from the sea, 6th January 2012, photograph by Nikolett Csorvasi
Above, an interglacial 'raised beach' deposit at 9 metres above sea-level
This pebble, shell and sand accumulation is "Ipswichian" in age.
The warming during the last interglacial period was due to natural causes.

These were basically changes in solar radiation hitting the earth, due to the tilt of the earth on its axis. 
We can use past climates as a natural experiment on the Earth’s systems, to consider the way it reacts to warming. 

This earlier warm period is useful to estimate what the future has in store, but had some different features.

The Eemian began when the previous glacial stage ended, and that glaciation was on a bigger scale than the more recent one that came before our interglacial, the Holocene.

New research has helped to explain the processes that happened as that earlier glacial stage ended.

Because more melt water ended up in the north Atlantic, the Arctic appears to have remained colder during the Eemian than it has during the Holocene.

Wednesday, 24 October 2018

Climate Change - 1816: The "Year Without a Summer" - Volcanic Cooling

The climate can react to sudden shocks.

The weather in 1816 was very strange. 

Spring arrived, but then everything seemed to turn backward, as cold temperatures returned. 

The sky seemed permanently overcast. 

The lack of sunlight became so severe that farmers lost their crops.

Food shortages were reported in Ireland, France, England, and the United States.

1816 became known as "The Year without a Summer" or "18-hundred-and-frozen-to-death".

It was over 100 years before anyone understood the reason for this weather disaster.

The eruption of an enormous volcano on a remote island in the Indian Ocean a year earlier had thrown enormous amounts of volcanic ash into the upper atmosphere.

The dust from Mount Tambora, which had erupted in early April 1815, had shrouded the globe. 

With sunlight blocked, 1816 did not have a normal summer.

In Switzerland, the dismal summer of 1816 led to the writing of a famous story. 

A group of writers, including Lord Byron, Percy Bysshe Shelley, and his future wife Mary, challenged each other to write dark tales, inspired by the gloomy and chilly weather.

During the miserable weather Mary Shelley wrote her classic novel Frankenstein.

This event was not unique.

Volcanic events can cool the Earth for a few years.

The large eruption of Mount Pinatubo caused a dip in global temperatures in the early 1990s:

Mount Pinatubo 1991

In the year 1258, there was a European famine across many countries, and this is now linked to a major eruption in 1257 on Lombok in Indonesia - it has a much bigger sulphate peak in the ice cores than Tambora, so it was a bigger eruption.

In the year 536 , a mysterious fog plunged Europe, the Middle East, and parts of Asia into darkness, day and night—for 18 months. Summer temperatures dropped 1.5°C to 2.5°C, initiating the coldest decade in the past 2300 years. Snow fell that summer in China; crops failed; people starved. 

Now, after analyzing volcanic glass particles in ice from a Swiss glacier, a team of researchers has identified the culprit: A cataclysmic volcano in Iceland spewed ash across the Northern Hemisphere early in 536.

Researchers have investigated how future volcanic eruptions might affect the current trend of global warming.

They produced this graph showing that even a period of very active vulcanism would not affect the long-term trend -


The red curve shows how the temperature evolves from year to year in a simulation without volcanic activity. The blue curve shows the result for the simulation of the study with largest volcanic activity.

This new research shows that strong volcanic eruptions would produce short periods of cooling, that would generally be followed by periods of accelerated warming, as the effects of the volcanic emissions subside, and the effects of CO2 emissions catch up. 


Tuesday, 23 October 2018

Climate Change - What's going on with the Gulf Stream?

The Gulf Stream transports vast amounts of heat north, from the equator to the pole, passing off the East Coast of the U.S. and into the North Atlantic.



The Northern Hemisphere winter of 2014-15 was the warmest on record globally, according to the National Oceanic and Atmospheric Administration. 

But one area of the North Atlantic was the coldest on record... shown in blue on this map.Land and Ocean Temperatures

This cold pool may be an indicator of a dramatic slowdown in the Gulf Stream.

A slowdown like this in the current has not happened for a very long time, perhaps as long as 1,000 years. 

It is possibly related to the melting of the Greenland ice sheet. 

The freshwater from the ice sheet is lighter than heavier, salty water that usually occupies that area. 

It tends to sit on top of the water, interfering with the sinking of dense, cold and salt-rich water.

650x366_10091611_oceancurrent


The Gulf Stream transports more water than "all the world's rivers combined," according to the National Oceanic and Atmospheric Administration.

A rapid slowdown in the current would increase the rate of sea level rise along the Mid-Atlantic and North-east coasts of the U.S. 

It could also bring much cooler conditions to parts of northern Europe.

This is still a matter needing more research.

Monday, 22 October 2018

Climate Change - Oil Geology

Oil is a fossil fuel.

It was formed from chemicals from ancient living things.

To make the chemicals in oil, the temperatures and pressures needed to be just right.

The oil (and gas) will only stay in the reservoir if there are suitable structures in the rocks:



The carbon compounds from the plants and animals have been trapped for hundreds of millions of years.

They have been burned to make carbon dioxide in a very short time.

The amount of carbon dioxide in the air has changed very quickly.

Diagram of how oil is made
Source: Library and Archives Canada
© Library and Archives Canada

Sunday, 21 October 2018

Climate Change - The link with mass extinctions

What is the worst-case scenario for climate change?

The geological record shows that when the atmosphere suddenly changes, there are big effects on living things.

Five major mass extinction events are recorded in the rock record of the last 600 million years.
The biggest extinction was at the end of the Permianaround 252 million years ago.
It is called the End-Permian mass extinction.


Only about 8% of species survived to live on in the Triassic Period.

Researchers have found evidence of a compound called fly ash, one of the products of coal combustion, in rocks laid down just before this extinction event. 

A large amount of coal had been burned over a period of tens of thousands of years.



The coal was burned by volcanic eruptions that happened in Siberia, which produced a large area of volcanic rocks called the Siberian Traps.

The burning actually happened underground, with the carbon dioxide and ash mixing with magma.



This produced vast amounts of CO2 which warmed the Earth and changed the chemistry of the oceans.

Saturday, 20 October 2018

Climate Change - The Medieval Warm Period and the Little Ice Age

Why can’t recent climate change just be an effect of 'natural causes'?

There have been climate changes in the past 2000 years.


People talk about times called the Medieval Warm Period and the Little Ice Age.


Careful research has shown that the current temperature is warmer than the Medieval Warm Period - temperatures between 1000 and 1100 AD were probably similar to parts of the 20th century, but 21st century temperatures are already warmer.


How does the Medieval Warm Period compare to current ...

The Medieval Warm Period may not even have been a global event - glaciers on Baffin Island were no smaller during that time.

A particularly cool period is often called the Little Ice Age.

However, the name "Little Ice Age" is now regarded by some scientistsas misleading.


The best estimate of the drop in temperature is, at most, 0.5°C, compared to the temperature decreases in "real" ice ages of about 8°C. 


Also, the "Little Ice Age" only lasted for 500 years at most, compared to the 20,000 years of the last ice age.


The start of that period is associated with the major volcanic eruption in 1257 of the Samalas volcano, next to Mount Rinjani on the island of Lombok, Indonesia.


Fig. 2.


This eruption was followed by famines in many places.

In 1258, a monk in England reported: "The north wind prevailed for several months… scarcely a small rare flower or shooting germ appeared, whence the hope of harvest was uncertain... Innumerable multitudes of poor people died, and their bodies were found lying all about swollen from want… 


The lowest temperatures in the "Little Ice Age", between about 1570 and 1730, were during a period of almost continuous smaller-scale volcanic activity.


The Industrial Revolutionwhen coal burning began on a large scale, started the recent rise in temperatures, reversing the longer-term very slow cooling trend.