Lecture 13: Anthropogenic Climate Change

Review:

• Seasonal cycles of light, nutrients, and chlorophyll for the temperature North Atlantic 

  • Light: dark in winter and fall, lighter in summer and spring 

  • Nutrients: high in winter and fall due to less dense waters making it easy for mixed layer depth, spring and summer are warmer waters so less nutrient rich because more stratification 

  • Chlorophyll: low in winter and fall because less light means less photosynthesis; on the other hand, high in summer and spring due to abundance of light but in summer, nutrients are depleted so it declines 

• Differences between El Nino and La Nina:

  • El Nino produces warmer waters in the eastern pacific and trade winds are weakened; more rainfall in eastern pacific but droughts in the west; leads to decreased productivity and fish die 

  • La nina produces colder waters and trade winds are stronger; there is less rain in the eastern pacific but more rain in the west; increase in productivity 

    • Colder = more chlorophyll since mixed deep layer is deepened 

• Observed anthropogenic climate change and future projections 

  • World is getting warmer due to global warming 

    • Increases are greater over land and polar zones; tend to be weaker in the ocean since the ocean modifies these changes 

    • Warming and salinity changes lead to increased stratification and this causes a decrease in nutrient delivery 

    • With increased stratification, there is less ventilation (less oxygen) in the ocean surface because everything is separated 

  • Hydrology is changing due to runoff patterns shifting

    • Mountains are accumulating snow but due to the warming of the earth, it melts earlier/faster causing runoff 

  • Oceans are getting warmer so abnormal blooms are occurring causing economic consequences (can be poisonous to aquatic life) 

    • Oceans are becoming more acidic, certain organisms cannot handle the acidity such as pterpod 

  • Greenhouse effect: atmosphere is transparent and trapping the radiation being emitted from earth (longer) so is warms the earth in general 

    • Sunlight that comes in is either absorbed by the surface or reflected by clouds 

    • Some absorbed by atmosphere and gets trapped, making climate increase 

  • Arctic ice is melting quickly due to the warming of the earth

    • Ice is much thinner and melts almost entirely during summer 

    • Causes the albedo to decrease since the surface is less reflective with less ice

    • Positive feedback as the ice melts and creates a dark surface that absorbs more heat and leads to more things melting 

      • Increase in sea level because when you warm water, it expands

      • There is not necessarily an increase of water being added because the ice was already there, just not melted 

  • Rainfall is hard to determine, lack data, fairly new field

    • Some areas are wetter and received more rain but others did not

    • Hard to tell because data is not conclusive with everything 

    • Extreme rainfall and flood events are more likely to occur in warmer climates 

  • Future predictions utilize a climate model that can predict the climate over a decade 

    • Newer models are now made that have higher spatial resolution

      • Represent more factors chemically, physically, and environmentally

      • Includes the biology and ecology of land.water

    • Can they be trusted?- with considerable confidence since the models are based off of accepted physical principles and they have worked in the past 

    • Sources of uncertainty: scale and resolution; imperfect understandings of natural processes; natural climate variability; unknown future emissions due to human activities 

• Impacts of climate change

  • On humans and society: 

    • Water supply: we get water from mountains and since climate is warmer, the ice is melting sooner and more runoff

    • Agriculture: increase in temperature means crops must be adapted to be able to handle the warmer climate or else humans have no food 

    • Human health: heat waves have killed thousands of people 

    • Infrastructure: sea levels are rising due to the water getting warmer, people need to be more mindful when building homes and buildings near oceans 

  • On marine ecosystems?

    • How do organisms respond to climate change?

      • Move in space or time, change behavior, acclimate through physiology, evolve, change in fitness and abundance 

    • Warming has increased stratification so there are less nutrients at the surface for phytoplankton 

      • Tropics and mid-latitudes (nutrient limited): less mixing and lower supply of nutrients so there are less plankton at the surface/in general

      • High latitudes (light limited): less mixing but increase in plankton at the surface to get all the light they can 

    • In light limited, high latitude regions of the ocean, anthropogenic climate change is projected to: increase net primary productivity because the plankton are forced to come to the surface due to the lack of nutrient delivery 

    • Biomass of diatoms will decrease since there is less nutrients due to increased stratification; thus, smaller phytoplankton will become dominant 

    • Export production: flux of particles out of the euphotic zone (uppermost surface where light penetrates)

      • Decrease globally but increases in high latitude where phytoplankton growth is light/temperature limited 

      • Decreases because warmer waters = more stratified

      • But areas with limited light are colder so upwelling can occur to bring the nutrients up 

    • Biological pump may be weakened: co2 levels increase and further warm climate since the plankton cannot take it in 

  • Subpolar: stratification increases, nutrient delivery to surface decreases, primary production increases, export production increases

  • Subtropics: stratification increases, nutrient delivery to surface deceases, primary production decreases, export production decreases 

  • increasing CO2 levels could hinder growth of some phytoplankton but help others 

  • Some phytoplankton blooms are occurring earlier than expected and they are moving/out of range