D4.3 Climate changeIB Biology HL: Revision notes

Anthropogenic emissions of carbon dioxide (fossil fuels, deforestation) and methane (livestock, rice paddies, landfill) must be limited. Antarctic ice cores show a positive correlation between carbon dioxide and temperature; correlation is not causation, but other evidence confirms the causal link.

Positive feedbacks amplify warming: carbon dioxide release from the deep ocean, loss of reflective snow and ice, faster decomposition of peat and permafrost organic matter, methane release from melting permafrost, and more droughts and fires. In boreal forest a tipping point is a switch from net carbon accumulation to net carbon loss, through drought, browning, fire and legacy carbon combustion.

Early break-out of landfast ice threatens emperor penguin (Aptenodytes forsteri) breeding; loss of sea ice removes resting platforms for walruses. Warmer surface water can prevent nutrient upwelling, reducing ocean primary production and energy flow through food chains. Species shift poleward and upslope: New Guinea montane birds moved uphill; North American trees show range contraction and northward spread.

On coral reefs, higher carbon dioxide causes ocean acidification and suppresses calcification; higher temperatures cause coral bleaching. Loss of corals causes reef ecosystem collapse.

Afforestation, forest regeneration and restoration of peat-forming wetlands store carbon. Peat forms in waterlogged soils (temperate, boreal and, very rapidly, some tropical ecosystems). Scientists debate whether non-native plantations or rewilding with native species is better.

Phenology is research into the timing of biological events such as flowering, budburst and bud set in deciduous trees, bird migration and nesting. The main cues are photoperiod (day length) and temperature.

Climate change alters temperature but not photoperiod. If one population in an ecosystem uses temperature as its cue and another uses photoperiod, their events drift apart and synchrony is disrupted:

• Arctic mouse-ear chickweed (Cerastium arcticum) grows earlier as it warms, but migrating reindeer (Rangifer tarandus) arrive at the same date, missing the most nutritious growth.
• Great tit (Parus major) nestlings in north European forests now hatch after the peak biomass of caterpillars, reducing breeding success.

Insects are ectotherms, so their development rate rises with temperature. Warmer, longer summers let the spruce bark beetle (Ips typographus or Dendroctonus micans) complete two or three generations a year instead of one. Populations build up rapidly, and drought-stressed spruce produce less defensive resin, so outbreaks kill large areas of forest, which then releases carbon.

Climate change alters selection pressures. In Finland the tawny owl (Strix aluco) has a heritable grey and brown morph. In snowy winters brown owls survive less well than grey owls; with less snow cover this disadvantage has largely disappeared, and the frequency of the brown morph has risen sharply. A change in allele frequency is evolution driven by climate change.