Present and potential impacts of climate change

Overview

Happening to mountain glaciers, glacial lake outburst flood and present impacts of increased heat on people.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What impacts are already being felt in high latitudes, and who is affected?

   Model answer

   The Arctic is warming several times faster than the global mean. Sea ice is thinner and forms later, which lengthens the open-water season for shipping and resource extraction but removes the platform that indigenous communities use for hunting and travel, and the hunting grounds of polar bears, walrus and seals. Thawing permafrost causes the ground to subside unevenly, cracking roads, runways, pipelines and buildings across northern Russia, Alaska and Canada and requiring expensive re-engineering. Loss of sea ice also exposes previously protected coasts to wave attack, so some Alaskan and Siberian settlements are eroding and have had to plan relocation. Traditional knowledge about ice conditions has become unreliable, which is a safety as well as a cultural loss.

2. 2

   What is happening to mountain glaciers, and why does it matter for people downstream?

   Model answer

   Mountain glaciers are retreating almost everywhere and losing mass in nearly every year measured. This matters because a glacier is a natural reservoir that stores winter precipitation as ice and releases it as meltwater in the warm, dry season when rainfall is least and demand is highest. Hundreds of millions of people in the Indus, Ganges and Brahmaputra basins, in Central Asia and in the Andes depend on that dry-season flow for irrigation, drinking water and hydroelectric power, and cities such as Lima and La Paz rely on it directly. Melting initially increases flow, which is deceptive, but once a glacier shrinks past a certain point the dry-season flow declines permanently, leaving a seasonal water gap that has to be filled by reservoirs or groundwater.

3. 3

   What is a glacial lake outburst flood?

   Model answer

   As a glacier retreats, meltwater often ponds behind the loose moraine ridge left at its former snout, forming a lake that grows year by year. The moraine is unconsolidated till and may contain buried ice, so it is a weak natural dam. If it is overtopped, undercut or destabilised, by a landslide or an ice avalanche into the lake or by an earthquake, it can fail suddenly and release many millions of cubic metres of water in a few hours. The resulting flood carries a huge load of debris down the valley, destroying settlements, farmland, bridges and hydroelectric installations far downstream with little or no warning. The hazard has grown as glaciers retreat and lakes multiply, notably in Nepal, Bhutan and Peru, and it is managed by monitoring lake levels and by artificially lowering the most dangerous lakes.

4. 4

   What are the present impacts of increased heat on people?

   Model answer

   Heatwaves already kill in large numbers, particularly among the elderly, the very young, those with cardiovascular or respiratory illness, and outdoor workers; the European heatwave of 2003 caused tens of thousands of excess deaths, and comparable events have recurred since. Heat reduces labour productivity in agriculture and construction, which matters most in tropical LEDCs where outdoor work dominates and air conditioning is unaffordable. It strains electricity systems as cooling demand peaks, causing blackouts precisely when cooling is most needed. Cities suffer most because the urban heat island adds several degrees, and the poorest districts, with least green space and worst housing, suffer most within cities. Heat also worsens air quality by promoting the formation of ground-level ozone.

5. 5

   What is happening to coral reefs, and why?

   Model answer

   Reefs are suffering repeated mass bleaching. Corals live in symbiosis with algae that provide most of their food and their colour; when water temperature exceeds the normal summer maximum by only one or two degrees for several weeks, the coral expels the algae, turns white and begins to starve. It can recover if conditions return to normal quickly, but not if the stress is prolonged or repeated. Events that were unknown before the 1980s have now struck the Great Barrier Reef repeatedly within a decade, leaving too little time for recovery between them. Ocean acidification compounds the problem by making it harder to build the calcium carbonate skeleton. The consequences reach people directly, since reefs support fisheries that feed millions, generate large tourism revenues, and absorb wave energy that would otherwise reach the coast.

6. 6

   What impacts are already being felt on low-lying coasts and small island states?

   Model answer

   Roughly 20 centimetres of sea-level rise has already made coastal flooding far more frequent, because a modest rise in mean level converts a rare extreme tide-and-surge combination into a routine one; some coasts now flood on high spring tides in calm weather. Salt water is intruding into coastal groundwater and into the soil, contaminating drinking water and reducing crop yields, which is a severe problem on low coral atolls where the fresh water is a thin lens floating on salt water. Erosion rates have increased and some low islands and shoreline villages have been abandoned. Communities in the deltas of Bangladesh, the Nile and the Mekong, and in atoll states such as Kiribati, Tuvalu and the Maldives, are the most exposed.

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