13, Flashcards
how is Antarctica effected by climate change
- different areas are behaving differently.
- On the Antarctic Peninsula, where climate is warming rapidly, 87% of glaciers are retreating but the area is small and the contribution to sea-level rise, a few centimetres per century, is comparable to that from Alaskan glaciers.
- The East Antarctic ice sheet appears close to balance, although increased snowfall may cause this area to thicken slowly in future. In West Antarctica, there is an area roughly the size of Texas where the ice sheet is thinning rapidly — the Amundsen Sea Embayment (ASE). Close to the coast in ASE, thinning rates are more than 1 metre per year.
What makes Antarctica so important
The vast, ice-covered Polar Regions are like a global thermostat that regulates the Earth’s climate system. The whiteness of the ice sheets help cool the atmosphere by reflecting heat from the Sun; the darkness of the polar oceans absorbs heat from the sun. Ice cold, salty water from the surface drops into the deep oceans to drive the ocean currents that carry heat around the globe. The Southern Ocean that surrounds Antarctica is a natural ‘sink’ that absorbs the greenhouse gas carbon dioxide from the atmosphere.
• Scientists know that the Antarctic ice sheet has grown and shrunk over geological history. Recent analysis of Antarctic ice cores reveal that during the last 800,000 years the Earth experienced eight glacial cycles (each with an ice age and warm period). Understanding this natural rhythm helps scientists get a better picture of what’s happening to the Earth’s climate today and what might happen in the future.
Is Antarctica melting?
The majority of long-term measurements from Antarctic research stations show no significant warming or cooling trends, and temperatures over most of the continent have been relatively stable over the past few decades. The effects of the ozone hole have shielded much of the Antarctic continent from the impact of ‘global warming’.
Does the hole in the ozone affect antarctic climate?
- We now know that the Antarctic ozone hole has had a profound effect on the Antarctic climate that extends far beyond increasing the levels of ultra-violet radiation.
- As stratospheric ozone amounts have fallen, temperatures above the continent have also dropped.
- This creates a bigger temperature difference between the tropics and the Antarctic which affects global weather patterns. For example, since 1980 the strength of winds over the Southern Ocean has increased by about 15%.
ANTARCTIC PENINSULA
the long mountainous landmass that projects from the main continent. Climate records from the west coast of the Antarctic Peninsula show that temperatures in this region have risen by nearly 3°C during the last 50 years — about five times the global average, and only matched in Alaska and Siberia. British Antarctic Survey research has shown also that near-surface sea temperatures to the west of the Peninsula have risen by over 1°C over a similar period. It is now accepted that the waters of the Antarctic Circumpolar Current are warming more rapidly than the global ocean as a whole.
Is human activity warming Antarctica?
Experiments with climate models suggest that human activity has contributed to temperature changes observed across Antarctica, including the rapid warming on the western side of the Antarctic Peninsula. However, these changes also reflect natural factors, such as variations in volcanic dust in the atmosphere and changes in the energy output of the Sun. But the eastern side of the Antarctic Peninsula is very sensitive to climate change. Stronger westerly winds in the northern Antarctic Peninsula, driven principally by human- induced climate change, were responsible for the marked regional summer warming that led to the well-publicised retreat and collapse of the northern Larsen Ice Shelf. In October 2006, the first direct evidence linking human activity to the collapse of northern Antarctic Peninsula ice shelves was reported in the Journal of Climate.
EVIDENCE
The ozone hole and global warming have changed Antarctic weather patterns such that strengthened westerly winds force warm air eastward over the natural barrier created by the Antarctic Peninsula’s 2km-high mountain chain. On summer days when this happens temperatures in the north-east Peninsula warm by around 5°C, creating the conditions that allowed the drainage of melt-water into crevasses on the Larsen Ice Shelf, a
key process that led to its break-up in 2002.
SEA LEVEL RISE
- 10 MIL PEOPLE AFFECTED EACH YR BY COASTA; FLOODING
- THIS WILL INCREASE TO 3OM BY 2080
- if sea-level were to rise by 44cm (a mid-range estimate) the number of people suffering would increase to more than 100m (10 x).
- In the UK, the replacement for the Thames Barrier and the 300km or so of sea defences that protect London need to be overhauled by 2030.
HOW MUCH DOES IT COST TO PROTECT LONDON AGAINST FLOODING?
The investment required to protect London against flooding depends heavily on sea-level rise, but could exceed £20 bn.
RATE OF SEA LEVEL RISING
3MM per YEAR
ICE SHEET AFFECTING SEA LEVEL
If glaciers and ice sheets shrink, ice that was held above sea level will find its way into the oceans. If ocean volume increases global sea level will rise. This has happened many times in geological history
ICE CORES
Ice cores are cylinders of ice drilled out of an ice sheet or glacier. Most ice core records come from Antarctica and Greenland, and the longest ice cores extend to 3km in depth. The oldest continuous ice core records to date extend 123,000 years in Greenland and 800,000 years in Antarctica. Ice cores contain information about past temperature, and about many other aspects of the environment. Crucially, the ice encloses small bubbles of air that contain a sample of the atmosphere — from these it is possible to measure directly the past concentration of gases (including carbon dioxide and methane) in the atmosphere
Greenhouse gases and the recent past
Direct and continuous measurements of carbon dioxide (CO2) in the atmosphere extend back only to the 1950s. Ice core measurements allow us to extend this way back into the past. In an Antarctic core (Law Dome) with a very high snowfall rate, it has been possible to measure concentrations in air from as recently as the 1980s that is already enclosed in bubbles within the ice. Comparison with measurements made at South Pole station show that the ice core acts as a faithful recorder of atmospheric concentrations (see Fig. 1), although we do have to be cautious, as artefacts can arise at sites with high concentrations of other impurities.
Antarctic ice cores show us that the concentration of CO2 was stable over the last millennium until the early 19th century. It then started to rise, and its concentration is now nearly 40% higher than it was before the industrial revolution (see Fig. 2). Other measurements (e.g. isotopic data) confirm that the increase must be due to emissions of CO2 from fossil fuel usage and deforestation. Measurements from older ice cores (discussed below) confirm that both the magnitude and rate of the recent increase are almost certainly unprecedented over the last 800,000 years. The fastest large natural increase measured in older ice cores is around 20ppmv (parts per million by volume) in 1000 years (a rate seen during Earth’s emergence from the last ice age around 12,000 years ago). CO2 concentration increased by the same amount, 20ppmv, in the last 11 years! Methane (CH4), another important greenhouse gas, also shows a huge and unprecedented increase in concentration over the last two centuries. Its concentration is now much more than double its pre-industrial level. This is mainly due to the increase in emissions from sources such as rice fields, ruminant animals and landfills, that comes on top of natural emissions from wetlands and other sources.
Natural climate changes: glacial-interglacial cycles
By measuring the ratios of different water isotopes in polar ice cores, we can determine how temperature in Antarctica and Greenland has changed in the past. The oldest ice core we have was drilled by the European Project for Ice Coring in Antarctica (EPICA) from Dome C on the Antarctic plateau. It extends back 800,000 years and shows a succession of long cold ‘glacial’ periods, interspersed roughly every 100,000 years by warm ‘interglacial’ periods (of which the last 11,000 years is the most recent). This succession of events is well- known from other records, and the coldest periods in Antarctica are the times when we had ice ages. Ice sheets extended over North America as far south as Wisconsin, and over Britain to south of The Wash.
The role of greenhouse gases in glacial-interglacial cycles
From the air in our oldest Antarctic ice core, we can see that CO2 changed in a remarkably similar way to Antarctic climate, with low concentrations during cold times, and high concentrations during warm periods (see Fig. 3). This is entirely consistent with the idea that temperature and CO2 are intimately linked, and each acts to amplify changes in the other (what we call a positive feedback).It is believed that the warmings out of glacial periods are paced by changes in Earth’s orbit around the Sun, but the tiny changes in climate this should cause are amplified, mainly by the resulting increase in CO2, and by the retreat of sea ice and ice sheets (which leads to less sunlight being reflected away). Looking at the warming out of the last glacial period in detail, we can see how remarkably closely Antarctic temperature and CO2 tracked each other.
It is often said that the temperature ‘leads’ the CO2 during the warming out of a glacial period. On the most recent records, there is a hint that the temperature started to rise slightly (at most a few tenths of a degree) before the CO2, as expected if changes in Earth’s orbit cause an initial small warming. But for most of the 6,000-year long ‘transition’, Antarctic temperature and CO2 rose together, consistent with the role of CO2 as an important amplifier of climate change (see Fig. 4). In our modern era, of course, it is human emissions of CO2 that are expected to kick-start the sequence of events. We see no examples in the ice core record of a major increase in CO2 that was not accompanied by an increase in temperature. Methane concentration also tracks the glacial-interglacial changes, probably because there were less wetlands in the colder, drier glacial periods.
