Global WarmingLecture 4 The case against
Caveats • As with last lecture, todays lecture is being used to present a single point of view. • YOU should be deciding what you do and don’t believe and WHY • We will discuss both sides next week.
Some sociological notes • A scientific consensus doesn’t mean that something is correct! • Climate is not just a scientific issue, it is a political one, few people don’t have vested interests
The claims • Massive, non-anthropogenic climate change has occurred in the past, and will happen in the future. • Human activity is dwarfed by natural processes which render the impact of e.g. fossil fuel burning on global climate negligible. • Evidence for recent warming depends critically on the data and time range chosen. • There is insufficient evidence to conclude that anthropogenic global warming is occurring.
Rapid variation Younger Dryas
Weather is not climate • Weather is often random and chaotic, records are broken all the time. • Climate is more stable. Typically dictated by e.g. average temperature/rainfull over a 30 year period (some places use 10).
Carbon sinks and sources • CO2 is absorbed by the ocean, photosynthesized in plants – these are carbon sinks • CO2 is produced naturally by decaying material, forest fires, volcanoes (huge, but uncertain effect).
The null hypothesis • There is insufficient evidence to refute a null hypothesis that all observed variations in global climate are natural.
Models: projections (not predictions) More on models and how they work in two weeks
What is in the models • Basic physics (fluids, conservation laws, radiative transfer etc). • Future predicted changes in e.g. land use, population, emissions growth (hugely uncertain) • Parameterized treatment of local processes • Work on ~200 km “cells”
Statistical significance • The significance of past temperature changes simply depends on the time period you look at. • The significance that human acts induce a change in forcing is marginally significant • Future predictions include huge uncertainties and allow for both warming and cooling.
Not necessarily a bad thing • Increased temperatures improve crop yields at moderate lattitudes, where lots of people live! • CO2 actual produces a carbon fertilization effect. • They decrease deaths from cold, which typically outweigh deaths from heat.