D4.3 Climate change

Anthropogenic climate change is driven here by human-caused increases in atmospheric carbon dioxide and methane, which absorb outgoing infrared radiation.

Higher concentrations strengthen greenhouse forcing, altering Earth's radiative balance and raising long-term mean temperature.

Antarctic ice cores show a long-term positive correlation between CO₂ and temperature, but correlation alone does not establish causal direction. Infrared absorption physics, observations and climate models provide the additional causal evidence.

One weather event cannot demonstrate climate causation; attribution uses long-term patterns and multiple independent evidence sources.

A positive climate feedback produces a change that reinforces the initial warming, making the response larger than the original forcing alone.

Warming melts reflective snow; exposed darker land absorbs more sunlight, causing additional warming and further melt.

Positive means self-reinforcing, not beneficial. Feedback strength and thresholds vary and do not imply one fixed rate of warming.

A boreal forest tipping point can occur when carbon uptake by growth falls below carbon released by mortality, decomposition and fire.

Warmer temperatures + reduced winter snowfall → drought stress → lower taiga primary production and forest browning → more frequent/intense fires → combustion of living biomass and legacy soil carbon → net carbon loss.

Released carbon strengthens warming, while tree loss reduces future uptake; these feedbacks can make recovery to the former forest state difficult.

Repeated severe fires can burn older stored carbon as well as current vegetation, while drought prevents conifer regeneration from replacing the lost sink.

A tipping point is a risk of persistent state change, not a precisely dated outcome for every boreal region; local moisture, species and management matter.

Climate warming changes polar habitat by causing earlier Antarctic landfast-ice breakout and reducing Arctic sea ice.

Ice is physical habitat, not only frozen water: its seasonal timing and position control access to breeding, resting and feeding areas.

Landfast ice is attached to coast, seabed shoals or grounded icebergs; sea-ice extent and ecological effects vary by region and season.

Warmer surface water strengthens density stratification and can change the timing and extent of ocean upwelling.

Upwelling brings cold nutrient-rich deep water into the sunlit surface. Stronger stratification resists vertical mixing, so fewer nutrients reach phytoplankton.

Surface warming → stronger stratification → reduced/delayed upwelling → lower surface nutrients → lower phytoplankton primary production → less energy entering marine food chains.

If a seasonal upwelling pulse weakens, phytoplankton and then zooplankton production can fall, reducing food available to migrating consumers.

Currents also respond to wind and salinity; one local season is insufficient to attribute a long-term circulation shift.

As temperature zones move, species may shift upslope or poleward if dispersal and suitable connected habitat allow them to track their climatic niche.

High-elevation species can run out of cooler habitat, while slow-growing trees may not disperse fast enough to match the speed of climate change.

A shifting observation is not automatically caused only by climate; land use, barriers, competition and survey effort must also be assessed.

Coral reefs are threatened when warming causes bleaching and altered seawater chemistry reduces calcification, while pollution and overfishing weaken recovery.

Heat disrupts coral–algal symbiosis; acidification lowers carbonate ion availability; local stressors reduce resilience and recruitment.

Separate direct heat stress, chemistry effects and local pressures before evaluating a reef outcome.; separate driver, mechanism, response and timescale

A marine heatwave expels symbiotic algae, bleaching coral; repeated heat before recovery raises mortality risk. This gives a concrete prediction from the stated climate condition.

Bleaching is a stress response, not immediate death; outcome depends on duration, species and recovery conditions. Interpret the result within the stated evidence and scenario limits.

Carbon sequestration transfers atmospheric carbon into a biological store and lowers atmospheric CO₂ only while that storage persists.

There is active debate over non-native plantations versus rewilding with native species: rapid carbon uptake must be weighed against biodiversity, resilience and permanence.

Rewetting drained peat reduces aerobic decomposition and allows long-term soil carbon accumulation to resume.

Sequestration complements emissions reduction; temporary uptake cannot offset continued fossil-carbon release one-for-one.

Phenology is the timing of recurring biological events such as flowering, migration, breeding or leaf-out.

Temperature, day length and resource cues control schedules. Climate warming can advance or delay events, changing overlap among interacting species.

Record the event, cue, date shift and interacting species before inferring ecological impact.; separate driver, mechanism, response and timescale

Warmer springs advance caterpillar emergence; a bird that migrates on a fixed cue may miss the food peak. This gives a concrete prediction from the stated climate condition.

A date shift alone is not a population decline; consequences depend on synchrony and alternative food. Interpret the result within the stated evidence and scenario limits.

Phenological synchrony is disrupted when interacting populations shift seasonal events by different amounts because their cues respond differently to climate change.

Reduced overlap can lower energy transfer, growth, fledgling mass or reproductive success even if both populations remain present.

Mismatch is about the timing overlap required for an interaction. Species may partly adjust behaviour or evolve, so the outcome is not automatically permanent.

Within their tolerance range, warmer seasons accelerate insect development and can increase the number of complete life cycles per year.

Spruce bark beetles such as Ips typographus or Dendroctonus micans can complete additional generations or attack periods when summers are longer and winters milder.

Warmer development period → faster egg–larva–pupa–adult cycle → more reproducing adults in the same year → more attacks on spruce phloem → greater probability that tree defences are overwhelmed.

A second annual generation can attack trees already weakened by the first, allowing fewer beetles to cause lethal phloem damage.

Warming is beneficial only within physiological limits; extreme heat, drought effects on hosts and predators can alter the outcome.

Climate change can cause evolution when it changes the relative fitness of heritable variants, shifting their frequencies across generations.

In southern Finland, milder winters and reduced snow changed camouflage conditions for tawny owl (Strix aluco) plumage variants. Dark brown owls gained relative success compared with pale grey owls.

The mapped local textbook reports dark brown owls increasing from about 30% to 50% of the population, while brown owls have higher mortality in severe snowy winters.

Snow cover declines → colour-dependent detection/feeding and survival change → heritable colour variants leave different numbers of offspring → variant frequency changes.

A one-season colour difference or phenotypic plasticity is not evolution; the response must be heritable and demonstrated as a population-frequency change over generations.