The scientific view is that the increase in global temperature should not exceed 2 degrees Celsius above pre-industrial level. If the global temperature increases beyond 3 degrees Celsius above the pre-industrial level, what can be its possible impact/impacts on the world? Select the correct answer using the code given below.

Answer: (b) 1 and 2 only

Land turning into a carbon source and coral die-off are the projected impacts.

Statement by statement

1. ✓ CORRECT Hot, dry forests and thawing soils can release more carbon than they absorb.

2. ✓ CORRECT Corals bleach and die at much lower warming — widespread mortality is expected.

3. ✗ WRONG “All” wetlands disappearing permanently is an overstatement.

4. ✗ WRONG Cereal farming would shift and fall in places, but not become impossible everywhere.

The idea

Today land plants and soils absorb roughly a quarter of the carbon dioxide we emit, so land is a net sink. Heat changes the balance. Decay in soil, forest fires and drought speed up faster than plant growth does, and beyond a point land gives out more carbon than it takes in.

Temperature rises past 3°C in models → Forests dry and burn; frozen soils thaw → Soil microbes release carbon faster → Land can release more than it absorbs → Land can turn from sink to source → Warming speeds up further

The trap

“All” and “anywhere in the world” — the absolute words give statements 3 and 4 away.

Elimination technique

Statement 3 says “all the global wetlands will permanently disappear” and statement 4 says “not be possible anywhere”. Absolute words usually mark the false statement in Environment PYQs. Dropping both leaves (a) and (b).

Also know

These are called tipping points: Amazon forest dieback, permafrost thaw, loss of the Greenland ice sheet. Corals are the most heat-sensitive large ecosystem: they bleach when the sea stays about 1°C above the usual summer maximum for a few weeks.