Weather and climate, Year 10: climate change

2.6

HintBetween two and three; closer to three.

The whyThrough the Quaternary, global temperature has swung between long cold glacials and shorter warm interglacials. The evidence comes from ice cores, ocean sediments, tree rings and pollen. We live in an interglacial, and the recent warming is much faster than those natural swings.

Milankovitch cycles

HintThey carry the surname of the Serbian scientist who calculated them.

The whyThe orbit stretches and rounds again about every 100,000 years, the tilt changes over about 41,000 years and the wobble takes about 26,000 years. Together they explain the timing of the glacial and interglacial periods. They are far too slow to explain the warming of the last 150 years.

Sulfur dioxide blasted high into the atmosphere forms a haze that reflects sunlight back to space

HintThe culprit is a gas from the eruption, working like a thin sunshade.

The whyAsh falls out of the air within days or weeks. The gas reaches the stratosphere, where it forms tiny droplets that stay for a year or more and bounce some sunlight away. Volcanoes also give out carbon dioxide, but only about 1% of the amount people emit.

Slightly higher than average

HintThe spots are a sign of an active star, not a fading one.

The whyThe change over a cycle is tiny, about a tenth of one per cent. Longer quiet spells with very few sunspots have been linked with cooler periods such as the Little Ice Age. Satellites have measured the Sun's output since 1978 and show no upward trend, so it cannot explain recent warming.

Fewer trees are left to absorb carbon dioxide

HintThink about what a living tree was doing every day before it was felled.

The whyGrowing trees take in carbon dioxide and store the carbon in wood. Clearing them releases that store and also removes the plants that were absorbing the gas. Geographers name deforestation, burning fossil fuels and agriculture as the three human causes of climate change.

orbit; volcanic; Sun

HintOne is about our path through space, one about our nearest star, one about the ground beneath us.

The whyThese natural factors explain the climate changes of the past, including the glacial periods. None of them explains the rapid warming since about 1850, which matches the rise in greenhouse gases from human activity.

Rising sea level could flood much of their land

HintThe highest ground there is only a few metres above the waves.

The whyGlobal sea level rose by about 20 cm between 1901 and 2018 and the rise is speeding up. On a coral island that brings more flooding in storms, salt in wells and farmland, and coastal erosion. In time whole communities may have to move.

Less meltwater, so water runs short in the dry season

HintThe ice acts as a savings account that pays out every summer.

The whyGlaciers store winter snow and release it as meltwater in the warm, dry months, when crops and cities need it most. A smaller glacier gives less. In the short term faster melting can cause floods; in the long term the supply dwindles.

Coral bleaching

HintThe second word is what a strong household cleaner does to a coloured cloth.

The whyThe algae give coral its colour and most of its food. If the water cools again soon, the coral can recover. If the heat lasts, the coral starves and dies, and the fish and people that depend on the reef lose out too.

They have less money to prepare, adapt and recover

HintWho can afford irrigation, stored food and imports when the rains fail?

The whyAn HIC can pay for reservoirs, irrigation, crop insurance and imported food. In an LIC more people rely directly on rain-fed farming for food and income, and governments have less to spend on help. So the same change in climate does unequal damage.

Mosquitoes can survive in places that used to be too cool for them

HintWhat limits where a cold-blooded insect is able to live and breed?

The whyThe insects that carry these diseases need warmth to breed. As temperatures rise, they can live further from the Equator and higher up mountains, bringing disease to people with little immunity or health care for it.

Climate change adaptation

HintLiving things do something with the same name to suit their habitat.

The whyExamples are growing crops that need less water, storing and saving water where rainfall is becoming less reliable, and building defences or raising homes where the sea is rising. The other approach, cutting the causes, is called mitigation. Both are needed.

Deep underground, in porous rock

HintOil and natural gas were found trapped in the same kind of place.

The whyThe gas is compressed, piped away and injected into rock that has tiny spaces to hold it, such as old oil and gas fields or rock filled with salty water. A layer of impermeable rock above stops it escaping. It is a form of mitigation because it keeps carbon dioxide out of the atmosphere.

2015; 2

HintThe meeting took place in the middle of the last decade; the limit is a small whole number.

The whyIt is a legally binding international treaty that came into force in November 2016. Each country sets its own targets for cutting emissions and is expected to strengthen them over time. International agreements matter because greenhouse gases from any country affect the whole world.

Grow well with less water

HintWhich resource is now in short supply for the plants?

The whyDrought-resistant varieties are one way of changing agricultural systems. Others are changing planting dates, growing different crops altogether and using irrigation that wastes less water. All are adaptation: they respond to the change and do nothing to slow it.

desalination

HintThe word is built from 'saline', with a prefix that means 'remove'.

The whyIt gives a supply that does not depend on rainfall, which is why it counts as managing water supply. It uses a great deal of energy and is expensive, so it is used mainly by wealthier countries. Cheaper ways to manage supply include storing water, moving it and wasting less.