Overview of Climate Change Science: Fundamentals and Recent DevelopmentsPrepared for the Climate Change and Adaptation Symposium John Merrill, URI GSO November 18, 2011
Talk organizationI’ll present observational evidence of global warming, startingwith cycling between glacial and interglacial conditions over thelast half million years.This will lead in to the role and impact of greenhouse gases,their recent buildup and consequent rapid changes, ending withinformation on how climate models are used to assess thesechanges.The ﬁgures are from the 2007 report of the IntergovernmentalPanel on Climate Change, a UN organization of scientists anddiplomats charged with bringing the best science to bear on theunderlying science and on policy issues.
Glacial-Interglacial Cycles - observational evidence Data on atmospheric gases, collected from polar ice cores. Shaded areas = Interglacial periods.
Gas concentrations rise/fall over 1000s of years. Middle curves: CO2 - red, CH4 (methane) - blue. Oxygen isotope data = ice volume and temperature. T scale, right.(IPCC 2007) Brief warm periods with high gas concentrations = Interglacials. Most of last 450 ky spent in glacial conditions.
Ice core and instrumental gas data - last 2000 years CO2 and CH4 concentrations over last 2 ky, including recent instrumental data. Grey bands indicate range over prior 450 ky.
Note CO2 and CH4 now far exceed paleo values. These are greenhouse gases. Together with water vapor, H2 O, they keep the earth warm. Emphasis on CO2 and CH4 - they are altered by humans, or anthropogenically. Increased greenhouse gas concentrations and other eﬀects shift the global(IPCC 2007) heat budget.
Induced heating from anthropogenic eﬀects - Summary Heating by greenhouse gases, and cooling by aerosols and land use changes, over last 255 years.
Top two bars are heating by changes in primary anthropogenic greenhouse gases. Land use change example: forest clearing. Aerosols are particulates, smoke, dust, haze. Changes in solar heating are smaller than uncertainty. Estimated heating minus cooling shown in brown bar.(IPCC 2007)
Schematic of global thermal energy balance Heating from sunlight in left half; cooling by emitted thermal energy on right. Multiple sources of data required for each quantity.
Quantitative summary of heat balance of earth. Thick bands on right indicate atmosphere emits almost as much as it absorbs. Greenhouse gases absorb infared energy, heating the atmosphere. Increased amounts of(IPCC 2007) these gases, increased temperatures.
Evidence of warming in air temperature records Global average land-surface air temperature over 1850 - 2003. Bars are individual years; curves are smoothed estimates by diﬀerent groups. Continued warming in recent years.
Climate model simulations background Simulations used to check our understanding of processes, and to predict state of climate in times to come. Numerical models simulate climate. Most signiﬁcant physical processes included. Multiple models, using diﬀerent approaches. Simulations for prior years compared with observations. Available computer power enables multidecadal runs. Processes can be included/excluded to highlight eﬀects.
Climate model simulations of temperature trends Black, observed temperature; color, model estimates. Bottom, only natural processes; top, including anthropogenic greenhouse gases.
Dozens of independent simulations of a century of climate. In blue at bottom a Hypothetical scenario: steady GHG amounts. In yellow/red at top Realistic scenario of increasing gases. Vertical lines indicate volcanic eruptions - transient cooling events. Increased gases must cause the observed warming.(IPCC 2007)
Recently observed trends - impacts of warming Arctic summer sea ice melt has reached record extent. Coming exploitation of Arctic fossil fuel and ﬁsheries resources - troubling implications. Rate of melting of Greenland and Arctic sea ice has increased and is accelerating. Warming of tundra - release of huge amounts of GHGs trapped there.
Additional observed trends The ocean’s heat content is increasing. Isaac’s talk. Droughts more frequent and more intense. Record high temperatures outnumber record lows by over 3:1. Midlatitude storm tracks migrating towards the poles. Climate zones are shifting toward the poles, by hundreds of miles. Floods becoming more frequent and more intense. Ocean acidiﬁcation impacting ﬁsh, corals and other biota.
Future scenarios simulated Surface warming increment vs. time in various scenarios. Numerals indicate number of model simulations aggregated.
The rate of temperature rise is increasing. That is, the warming is accelerating. 5◦ C range = 9◦ F change. Lleveling oﬀ only with drastic changes, e.g. B1. Temperature increase expected even if all emissions stopped now.(IPCC 2007)
IPCC is a process as much as a group. Their next Report is being drafted now, and is to be released in June, 2013. Emissions of GHGs have exceeded targets everywhere and always, even with curtailment steps. Cautious scientists see important impacts as “virtually certain”.(Wickford, 2011 - J. Denton)