Tuesday, 30 April 2019

Climate Change - The Pliocene Rebooted?

Atmospheric carbon dioxide concentration is now over 400 parts per million (ppm).


It last reached similar levels during the Pliocene, 5.3-2.6 million years ago.


During this period, the area around the North Pole was much warmer and wetter than it is now.



Summer temperatures in the Arctic were around 15 degrees C, which is about 8 degrees C warmer than they are now.

Global average temperatures were 2-3°C warmer than today.

Of course, there were no modern humans at that time.



Hominids of the Pliocene

Nor was there a global system of food supply relying on stable climates for agriculture.


For more on research into the climate of the Pliocene, and what it can tell us about the likely effects of 400 ppm CO2, "Science News" has a very good article.  


Another paper: "Pliocene and Eocene provide best analogs for near-future climates" - Burke et al, 2018 makes these points:


"We are effectively rewinding the climate clock by approximately 50 million years,reversing a multimillion year cooling trend in less than two centuries."
 "by 2030 CE, future climates most closely resemble Mid-Pliocene climates, and by 2150 CE, they most closely resemble Eocene climates."

Monday, 29 April 2019

Climate Change - Permafrost and greenhouse gases

Arctic permafrost – ground that has been frozen for many thousands of years – is now thawing because of global climate change.

“The release of greenhouse gases resulting from thawing Arctic permafrost could have catastrophic global consequences,” said Dr. Max Holmes, a Senior Scientist at the Woods Hole Research Center (WHRC).


Greenhouse gases and permafrost.  

Thawing permafrost releases greenhouse gases (carbon dioxide and methane) into the atmosphere, which accelerate climate change, which in turn cause more thawing of the permafrost. 

This may be a fairly slow process, and there is a lot more research to be done in this area.

Sunday, 28 April 2019

Climate Change - Oceania

Oceania is a region made up of thousands of islands throughout the Central and South Pacific Ocean. 

It includes Australia, the smallest continent in terms of total land area.


Many of the nations in Oceania are Small Island Developing States (SIDS).


Many scientists say that Oceania is more vulnerable than most parts of the Earth to climate change, because of its climate and geography. 

The heavily coastal populations of the continent’s small islands are vulnerable to flooding and erosion because of sea level rise. 


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

Five of the Solomon Islands have been swallowed whole by rising sea levels between 1947 and 2014. 
"It’s a perfect storm,” says Simon Albert of the University of Queensland. “There’s the background level of global sea-level rise, and then the added pressure of a natural trade wind cycle that has been physically pushing water into the Western Pacific."
Albert and his colleagues analysed aerial and satellite images from 1947 to 2014 to study the effects of creeping sea levels on the coastlines of 33 reef islands in the Solomons.

Five islands present in 1947, ranging in size from 1 to 5 hectares, had completely disappeared by 2014.
Another six islands had shrunk by 20 to 62 per cent in the same period, confirming anecdotal reports of people living in the area.
Homes in Solomon Islands close to edge of sea
The most populated of these, Nuatambu Island, is home to 25 families, who have witnessed 11 houses wash into the sea since 2011.
Fiji’s shoreline has been receding about 15 centimetres per year over the last 90 years.

Samoa has lost about half a metre per year during that same time span. 

The global sea level graph is from this paper: 
"Temperature-driven global sea-level variability"

Saturday, 27 April 2019

Climate Change - Why isn't every year a record year?

Heat can affect things without causing a temperature rise.

Extra heat can be used in ‘changing state’ instead of raising temperature.
A change of state could be … a solid melting to a liquid
Or a liquid evaporating to a gas.

So heat is needed to change ice at zero degrees C to water at zero degrees C.
And to change water into water vapour….. without raising the temperature.
Scientists call the heat used to change state latent heat.
Also, there are natural variations in the global climate, El Nino events being the ones that affect world temperature the most.

The opposite to 'El Nino' is 'La Nina', a cooling effect.
If global temperatures are plotted on a graph in a way that shows these variations, it makes the overall warming trend very obvious.
Bar chart of temperature anomalies 1880-2015 indicating El Niñe phase
Every La Nina year since 1998 has been warmer than every El Nino year before 1995.

As the Earth warms, each El Nino event 'rides' on a higher base-line global temperature:
2017 was the warmest non-El Nino year in the modern record.



This chart shows global temperatures month by month, coded according to El Nino and La Nina, with neutral conditions in grey.

Friday, 26 April 2019

Climate Change - Deltas at risk

Deltas often form when rivers reach the sea.

The river can carry sand and mud when it is flowing fast.

As the water enters the sea, it slows down, and the sediment drops to make the delta.


Many deltas are at risk from climate change.   This map shows the levels of risk.
Deltas often form when rivers reach the sea.

The river can carry sand and mud when it is flowing fast.

As the water enters the sea, it slows down, and the sediment drops to make the delta.


Many deltas are at risk from climate change.   This map shows the levels of risk.


An estimated 80 percent of the world's megacities are located in fragile river deltas.   A megacity has a population of over 10 million people.

Over 500 million people live on deltas.

Why are deltas at risk?

One reason is rising sea level, which wears away the delta from the front.


An estimated 80 percent of the world's megacities are located in fragile river deltas.   A megacity has a population of over 10 million people.

Over 500 million people live on deltas.

Why are deltas at risk?

One reason is rising sea level, which wears away the delta from the front.

Thursday, 25 April 2019

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.

Wednesday, 24 April 2019

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.

Tuesday, 23 April 2019

Climate Change - The Palaeocene-Eocene Thermal Maximum

The geological record contains examples of major temperature changes, associated with changes in atmospheric CO2.


Matthew Huber at Purdue University calculated that warming slightly in excess of 10 degrees C—like that of the PETM and of pessimistic scenarios for future fossil-fuel burning—could render large portions of the planet uninhabitable for many creatures. He has said:
"There used to be subtropical forests near the poles 50 million years ago, and that doesn’t sound so bad.
"But the fossil record closer to the equator is really poor, and that may be an indication that life was extremely stressed during these warm periods.
"If over half the surface area of the planet becomes inhospitable, it will not render Earth uninhabitable, but it will be unrecognizable and existentially challenging for the majority of the people, species and communities on Earth."
Some researchers suggest the Palaeocene-Eocene Thermal Maximum, might be partly connected to an impact event that ignited forests.

During the PETM, a massive influx of carbon flooded the atmosphere and Earth warmed by 5 - 8 C degrees.

A recent research paper contains this quote:
"Given currently available records, we demonstrate that the present anthropogenic carbon release rate is unprecedented throughout the Cenozoic (past 66 million years)."
This graph compares the current situation with the PETM event around 56 million years ago:
We are doing something very extraordinary......

At current emissions rates, we’re just five generations away from creating an atmosphere the likes of which hasn’t been seen in 56 million years.

There are a number of other suggestions about how all the carbon compounds were added to the atmosphere to cause the PETM.

One is that the vulcanism along the newly-rifting Atlantic margins (producing the Atlantic Ocean basin) broke through various fossil fuel deposits such as oil and gas reservoirs.
Another is that stored methane was released from the oceans, again perhaps due to heating caused by that vulcanism.
Another is that a large shallow seaway that cut across a continent may have become cut off and then dried out; this exposed lots of peat-type material that became oxidised and hence produced lots of CO2.

Monday, 22 April 2019

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 a layer of electrons, 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, 21 April 2019

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 Vatnajökull 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, 20 April 2019

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, 19 April 2019

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.