💾 Archived View for gmi.noulin.net › mobileNews › 5644.gmi captured on 2021-12-05 at 23:47:19. Gemini links have been rewritten to link to archived content

View Raw

More Information

⬅️ Previous capture (2021-12-03)

➡️ Next capture (2023-01-29)

-=-=-=-=-=-=-

What is climate change?

22 October 2015

From the section Science & Environment

In December, officials from across the world will gather in Paris, France, to

try to hammer out a deal to tackle global warming. Here's what we know and

don't know about the Earth's changing climate.

What is climate change?

The planet's climate has constantly been changing over geological time. The

global average temperature today is about 15C, though geological evidence

suggests it has been much higher and lower in the past.

However, the current period of warming is occurring more rapidly than many past

events. Scientists are concerned that the natural fluctuation, or variability,

is being overtaken by a rapid human-induced warming that has serious

implications for the stability of the planet's climate.

What is the "greenhouse effect"?

The greenhouse effect refers to the way the Earth's atmosphere traps some of

the energy from the Sun. Solar energy radiating back out to space from the

Earth's surface is absorbed by atmospheric greenhouse gases and re-emitted in

all directions.

The energy that radiates back down to the planet heats both the lower

atmosphere and the surface. Without this effect, the Earth would be about 30C

colder, making our planet hostile to life.

Scientists believe we are adding to the natural greenhouse effect with gases

released from industry and agriculture (known as emissions), trapping more

energy and increasing the temperature. This is commonly referred to as global

warming or climate change.

The most important of these greenhouse gases in terms of its contribution to

warming is water vapour, but concentrations show little change and it persists

in the atmosphere for only a few days.

On the other hand, carbon dioxide (CO2) persists for much longer (it would take

hundreds of years for it to return to pre-industrial levels). In addition,

there is only so much CO2 that can be soaked up by natural reservoirs such as

the oceans.

Most man-made emissions of CO2 are through the burning of fossil fuels, as well

as through cutting down carbon-absorbing forests. Other greenhouse gases such

as methane and nitrous oxide are also released through human activities, but

their overall abundance is small compared with carbon dioxide.

Since the industrial revolution began in 1750, CO2 levels have risen by more

than 30% and methane levels have risen more than 140%. The concentration of CO2

in the atmosphere is now higher than at any time in at least 800,000 years.

What is the evidence for warming?

Temperature records going back to the late 19th Century show that the average

temperature of the Earth's surface has increased by about 0.8C (1.4F) in the

last 100 years. About 0.6C (1.0F) of this warming occurred in the last three

decades.

Satellite data shows an average increase in global sea levels of some 3mm per

year in recent decades. A large proportion of the change in sea level is

accounted for by the thermal expansion of seawater. As seawater warms up, the

molecules become less densely packed, causing an increase in the volume of the

ocean.

But the melting of mountain glaciers and the retreat of polar ice sheets are

also important contributors. Most glaciers in temperate regions of the world

and along the Antarctic Peninsula are in retreat. Since 1979, satellite records

show a dramatic decline in Arctic sea-ice extent, at an annual rate of 4% per

decade. In 2012, the ice extent reached a record minimum that was 50% lower

than the 1979-2000 average.

The Greenland Ice Sheet has experienced record melting in recent years; if the

entire 2.8 million cu km sheet were to melt, it would raise sea levels by 6m.

Satellite data shows the West Antarctic Ice Sheet is also losing mass, and a

recent study indicated that East Antarctica, which had displayed no clear

warming or cooling trend, may also have started to lose mass in the last few

years. But scientists are not expecting dramatic changes. In some places, mass

may actually increase as warming temperatures drive the production of more

snows.

The effects of a changing climate can also be seen in vegetation and land

animals. These include earlier flowering and fruiting times for plants and

changes in the territories (or ranges) occupied by animals.

What about the pause?

In the last few years, there has been a lot of talk about a pause in global

warming. Commentators argued that since 1998, there had been no significant

global warming despite ever increasing amounts of carbon dioxide being emitted.

Scientists have tried to explain this in a number of ways.

These include:

variations in the Sun's energy output

a decline in atmospheric water vapour

greater storage of heat by the oceans.

But so far, there is no general consensus on the precise mechanism behind the

pause.

Sceptics highlight the pause as an example of the fallibility of predictions

based on computer climate models. On the other hand, climate scientists point

out that the hiatus occurs in just one component of the climate system - the

global mean surface temperature - and that other indicators, such as melting

ice and changes to plant and animal life, demonstrate that the Earth has

continued to warm.

How much will temperatures rise in future?

In its 2007 assessment, the Intergovernmental Panel on Climate Change (IPCC)

forecast a global temperature increase of between 1.8C and 4C by 2100.

Even if we cut greenhouse gas emissions dramatically now, scientists say the

effects will continue because parts of the climate system, particularly large

bodies of water and ice, can take hundreds of years to respond to changes in

temperature. It also takes greenhouse gases decades to be removed from the

atmosphere.

How will climate change affect us?

The scale of potential impacts is uncertain. The changes could drive freshwater

shortages, bring sweeping changes in food production conditions, and increase

the number of deaths from floods, storms, heat waves and droughts. This is

because climate change is expected to increase the frequency of extreme weather

events - though linking any single event to global warming is complicated.

Scientists forecast more rainfall overall, but say the risk of drought in

inland areas during hot summers will increase. More flooding is expected from

storms and rising sea levels. There are, however, likely to be very strong

regional variations in these patterns.

Poorer countries, which are least equipped to deal with rapid change, could

suffer the most.

Plant and animal extinctions are predicted as habitats change faster than

species can adapt, and the World Health Organization (WHO) has warned that the

health of millions could be threatened by increases in malaria, water-borne

disease and malnutrition.

As an increased amount of CO2 is released into the atmosphere, there is

increased uptake of CO2 by the oceans, and this leads to them becoming more

acidic. This ongoing process of acidification could pose major problems for the

world's coral reefs, as the changes in chemistry prevent corals from forming a

calcified skeleton, which is essential for their survival.

Computer models are used to study the dynamics of the Earth's climate and make

projections about future temperature change. But these climate models differ on

"climate sensitivity" - the amount of warming or cooling that occurs as a

particular factor, such as CO2. goes up or down.

Models also differ in the way that they express "climate feedbacks".

Global warming will cause some changes that look likely to create further

heating, such as the release of large quantities of the greenhouse gas methane

as permafrost (permanently frozen soil found mainly in the Arctic) melts. This

is known as a positive climate feedback.

But negative feedbacks exist that could offset warming. Various "reservoirs" on

Earth absorb CO2 as part of the carbon cycle - the process through which carbon

is exchanged between, for example, the oceans and the land.

The question is: how will these balance out?