Climate change

anthropogenic causes of climate change

• methane and CO2 are most significant greenhouse gases

  • greenhouse gases absorb heat

• anthropogenic emissions of CO2

  • combustion of fossil fuels

  • burning of biomass during deforestation

  • increases frequency of forest fires

  • drainage or burning of peat

• anthropogenic sources of methane

  • anaerobic decomposition of organic matter in landfills

  • leaks during fossil fuel extraction

  • bubbles of methane released from melting permafrost

positive feedback in global warming

• global warming is amplified by positive feedback cycles, as an increase in earth’s temperature causes increases in factors that cause warming

• deep ocean CO2 release

  • global warming causing temperatures of oceans to rise, reducing solubility of CO2 in water, releasing it from the deep oceans into the atmosphere, contributing to GH effect

• reflection of sunlight

  • snow and ice are white, so reflect solar radiation back to space

  • snow and ice are melting with global warming and are being replaced by darker materials which absorb radiation, increasing warming

• decomposition of peat

  • saprotrophs decomposition speeds up with increasing temp, cell respiration releases CO2

• permafrost (soil that remains frozen throughout the year)

  • any dead organic matter in permafrost remains undecomposed

  • with higher temps soils melt, allowing methanogenic microbes to break down dead organic matter, releasing methane

• increase in droughts and forest fires

  • increased temps lead to drier, more fire-prone conditions so forest fires more frequent and severe

  • CO2 emissions from combustion are increased, less plants to absorb CO2 by photosynthesis

effects of climate change on boreal forests

• boreal forests are carbon sinks because carbon is stored in biomass of conifer trees

• during cold conditions, it’s digested by saprotrophs more slowly than produced

• with climate change, summers in boreal forests have become warmer and drier, resulting in fires and huge emissions of CO2 from combustion of legacy carbon

• as global temps rise, a tipping point could be reached beyond which boreal forests change from being carbon sinks to sources, meaning they contribute to global warming instead of removing CO2 from atmosphere

melting of polar ice caps

• extent of landfast (attached to shore) and sea ice is reducing due to global warming

• has impacts for animals:

• emperor penguins

  • breed on landfast ice in antarctic

  • climate change is making the extent of landfast ice very variable, making it difficult for emperor penguins to choose where they can breed

• walruses

  • use sea ice to rest between feeding sessions from rough seas and evade predators. sea ice expands broader range of feeding site

  • also use sea ice for breeding and nursing their young

  • global warming is reducing sea ice so land-based walruses have to make more feeding trips to areas further from shore, expending a lot of energy

changes in ocean currents

• warmer, less dense water floats on top of denser, colder, saltier water

• rotation of earth and winds cause currents to bring colder, deeper water towards the coast

  • this water is forced up to the surface, displacing warmer water

  • thus causes an upwelling of mineral nutrients, increasing growth of producers and hence availability of food for consumers

  • upwelling supports abundant marine life and makes very productive biological communities

• if surface water becomes warmer due to global warming, there tends to be less upwelling, reducing availability of mineral nutrients and therefore productivity

shifting climate zones

• the world is divided into climate zones:

  • polar

  • temperate (intermediate temps)

  • dry

  • tropical

• climate change is making many parts of the world warmer, so temperate zones are moving further towards the poles

• plants and animals that are adapted to temperate zones thus have to move their ranges towards the poles - poleward range shift

  • animals may do this by migration, plants are sessile so a range change is achieved by death where its too hot and colonisation where its cooler

• on mountains, climate becomes colder as altitude increases, species adapted to temperate zone on mountain have to move upslope as global warming shifts zones upwards - upslope range shift

poleward range shift example

• temperate tree species in North America are shifting northwards

• shown by large study of seed production and seedling survival rate in tree species

upslope range shift example

• temperate zone montane bird in New Guinea

• upper altitude limit of the ranges of 20 species has shifted upslope 650 meters between 1969 and 2013

threats to coral reefs

• emissions of carbon dioxide affect oceans by reducing their pH making oceans more acidic

• marine animals that deposit calcium carbonate in their skeletons need to absorb carbonate ions from seawater

• dissolved carbon dioxide makes carbonate concentration even lower due to the chemical reactions it undergoes

  • as more CO2 dissolves, more carbonic acid (H2CO3) forms and dissociates, & more hydrogen carbonate ions form and dissociate, resulting in increasing H+ in water hence more acidic

  • this makes difficult for reef-building corals to absorb carbonate and calcify their skeletons

• coral bleaching:

  • corals are mutualistic with algae zooxanthellae, coral provides safety, algae provides carbs and oxygen made by photosynthesis

  • when water becomes too warm, zooxanthellae are ejected leading to loss of colour

• coral species with calcium carbonate skeletons are the keystones of the reef, their loss would cause collapse of reef ecosystems globally

carbon sequestration

• carbon sequestration: capture and storage of CO2 from the atmosphere. 2 processes do this:

  • accumulation of biomass, produced in ecosystems by photosynthesis

  • accumulation of undecomposed organic matter, especially peat in wetlands

• there is currently an urgent need for carbon sequestration to bring back atmospheric CO2 concs back to normal

• approaches to enhance natural processes that sequester carbon:

  • afforestation

  • restoration of wetlands

afforestation

• planting trees in areas where they currently don’t exist

• this should only be done where forests are the natural ecosystem

• there is active debate over whether non-native or native species are best for carbon sequestration

  • native species have evolved to be adapted to conditions in that area so should grow rapidly

  • non-native species may be better adapted due to climate change

restoration of wetlands

• peat is partially decayed organic matter that forms in waterlogged ecosystems in both temperate and boreal zones, and forms very rapidly in some tropical ecosystems

• peatlands are huge carbon sink, but in many years have been drained to convert the land to agriculture

• can be re-established so carbon sequestration restarts

phenology

• organisms are adapted to carry out stages in their life cycle at most appropriate times of the year

  • phenology is studying the timing of seasonal events

• cues exist for organisms to determine when the appropriate time of year has arrived:

• photoperiod:

  • length of daylight during 24-hour period

  • follows the same cycle of change

  • plants an measure length of night, and many use it to time flowering

  • birds also use it to time migration and egg-laying

• temperature:

  • follows annual cycle of warming and cooling

  • warm temps in spring advance the dates of egg-laying in birds and bud-burst in deciduous trees

climate change and phenology

• events timed by temperature are affected by global warming

• e.g arrival of migrating reindeer

  • spring migration coincides with emergence and growth of arctic mouse-ear chickweed

  • allows females secreting milk for children to obtain enough food

  • climate change has lead to mismatch between plant growth and reindeer migration, so reindeer less able to meet their needs

• e.g growth of great tit

  • great tit feeds its young on caterpillars

  • caterpillar biomass now peaks much earlier in spring. the mean date of egg-laying has also become earlier but not by as much

climate change and insect life cycles

• insects vary how long their life cycle takes, in some species this cycle has become shorter due to global warming

• e.g spruce bark beetle

  • native to forest in north america

  • feed on bark of spruce trees

  • usually has a 1-3 year life cycle, but warmer temperatures have reduced the average time, increasing population growth

  • health of spruce trees has decline due to droughts, so more trees are succumbing to beetle attacks, leading to death of millions of spruce trees

climate change and evolution

• global warming is changing the adaptations living organisms need to thrive

• many traits are now subject to directional selection

• e.g tawny owl

  • varies in colour, from brown to pale grey, this is heritable trait

  • pale grey variant is better camouflaged in snow, but winters have become milder in Finland reducing snow cover

  • the brown tawny owl population has now more than doubled