Lecture 3 - Evidence for climate change and its impacts on terrestrial ecosystems

Nathalie Seddon

8 observed indicators of global climate change

• higher global air and sea temperatures

• changing patterns of rainfall

• retreating glaciers

• declining sea ice in the artic

• declining ice sheets in greenland and antarctic

• sea level rise

• increasing frequency/ and or of extreme events

• signatures from the living world/biosphere: timing of life cycle events and shifts in ranges

by how much have the global average surface temperatures increased since 1990

1.2 °C

what is significant about the years between 2015-2024

ten warmest years on record

what is meant by an anomaly

a difference between the observed temperature and a long term average temperature for a specific location and time of year

how is rainfall changing with global warming and why

• frequency of precipitation events on land has increased consistent with higher temperatures which result in more atmospheric water vapour

• more intense and longer droughts particularly in the tropics and subtropics

what is meant by arctic amplification

the fact that the arctic and antarctic are warming 4 times faster than the rest of the globe

what are the causes of arctic amplification

• many interacting factors

  • eg Ice-albedo feedback: melting ice reduces reflecting surfaces thus increasing the amount of light/heat absorption

how much ice do we loose from the melting of ice sheets a year

approx 281 billion metric tones a year

how much have sea levels risen by

20-25cm since 1901

how much more water does the atmosphere hold per 1 celcius increase in temp

7%

how is climate change affecting tropical cyclones

• getting stronger

• heavier rainfall in TC

• proportion of major cyclones (Cat 3-5) is on the rise

• the strongest ever reccorded TC are occuring currently

what is uncertain about the effect of climate change on tropical cyclones

its effect on frequency because we dont have long term data as satellites are a recent invention

why are we seeing these changes in tropical cyclones

increases in sea surface temperatures which changes the air pressure and dynamics above oceans

what is another example of an extreme event which has been on the rise

wild fires

what are the mechanisms that result in increased fire weather (conditions which make wild fires more likely)

• drier fuel due to increased temp

• earlier snow melt

• longer droughts

what are the three main “buckets” of signatures of climate change from the biosphere

• changes in ecosystem structure

• changes in timing (phenology)

• changes in species range shifts

what is an example of changes in species phenologies in plants

• the changing timing of cherry blossom flowering (cultural event), evidence from records that timing was constant for ~600 years until 1952

• european grape harvest, constant for 500 years until 2003

what is an example of changing phenologies in birds

changing in breeding periods in great tits in wytham woods

how about for insects

since 1970, 70% of butterful species have advanced first flight date by 24 days

what about amphibians

they are spawning and chorusing earlier

how are rangeshifts changing

• tree-lines shifting

• flora and animals expanding ranges upslopes

what is a term that describes how community structures are changing and what does it mean

thermophilisation - process by which ecosystems or communities of species are increasingly dominated by organisms that re better adapted to warmer temperatures

how is global warming affecting community structures in marine ecosystems

• increase in marine heatwaves 

• causing mass mortalities especially in coral