lecture 10

• It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.
• The scale of recent changes across the climate system as a whole and the present state of many aspects of the climate system are unprecedented over many centuries to many thousands of years.
• Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since the 5th Assessment Report (AR5).
• Improved knowledge of climate processes, paleoclimate evidence and the response of the climate system to increasing radiative forcing gives a best estimate of equilibrium climate sensitivity of 3°C, with a narrower range compared to AR5.
• >99% of all climate scientists agree that human induced climate change is real
• Natural greenhouse effect


  Acting as a "blanket" around the globe, keeping average global temperatures stable around 15oC (without it the average temperature would have been -18oC)
• Anthropogenic greenhouse effect


  With increasing greenhouse gas emissions from burning of fossil fuels, deforestation, farming etc, the earth's energy balance is changing, and more heat radiation stays in the atmosphere – with increasing global temperature as a result
• Sources of Greenhouse Gas Emissions


  • Energy/electricity-, transportation-, residential and commercial buildings- and industry sectors (e.g. steel and cement production) makes up ~2/3 of the GHG emissions
  • Agriculture and forestry sectors the other 1/3 of the emissions: Deforestation - release of CO2, Farmed land - release CO2, CH4 and N2O, Animal farming - release CH4
• 85% of the anthropogenic CO2 emissions come from burning of coal, oil and natural gas.
• Today we release ~10Gt of Carbon (=~36Gt of CO2) per year
• Atmospheric CO2 concentrations are now >410ppm
• The famous "hockey-stick" curve of earth's temperature record for past 1000 yrs from 1999 by climate scientists Prof. Mann, Bradley and Hughes shows a clear correlation between CO2 increase from the industrial revolution and simultaneous increase of temperature
• 14 of the 15 hottest years on record have occurred since 2000 (UN report)
• Last decade (2010-2020) is the hottest on record
• 2020 was 2nd hottest year on record
• Average global temperature has increased with ~1oC since pre-industrial times
• However, it has increased with 0.18oC per decade since 1981
• GHG levels are now the highest in 800 000 yrs
• Annual rate of increase in CO2 in the past 60 years = 100 times faster than previous natural increases
• Over the past decade, the growth rate has been closer to 2.3 ppm per year
• May 2020 was the hottest month every recorded (141 yrs of measurements), with 1.6 degrees C above 20th Century average
• Data shows that the number of extreme temperature events has gone up over the past 60 yrs.
• Climate Change is one of the biggest challenges facing humanity in the 21st century
• Potential direct impacts of Climate Change


  • Extreme weather
  • Sea-level rise
  • Ocean circulation
  • Extinction of species
  • Food insecurity
  • Human Health
  • Political instability
• Predicted costs associated with Climate Change until end of century: $600 Trillion
• 2oC increase in global temperatures: a "tipping point"?
• Climate "feedback mechanisms"


  • Ice-albedo (reflectiveness) is decreasing –> strong positive feedback loop
  • Precipitation (due to increase in water vapor from evaporation) could increase growth and CO2 uptake –> negative feedback loop
  • Cloud formation (due to increase in water vapor from evaporation) will increase albedo in atmosphere -> negative feedback
  • Methane (GHG) release from arctic tundra – potential strong positive feedback
  • Volcanic activity is not affected by climate change but can lead to emissions of reflecting particles in atmosphere -> negative feedback
• Current sea level rise is about 3 mm/year worldwide (30cm/century). IPCC report
• Although, CO2 emissions have levelled out in some parts of the developed world, emissions are still increasing in many developing nations as their economy growths. This in combination with rapid population growth in these countries poses a "double challenge".
• Developed nations need to help developing nations to bypass the dependence on fossil fuel and to ensure that their economies grow through sustainable development
• Climate change needs action at


  • Global, regional, national and local levels