global warming lecture 4 the case against. caveats as with last lecture, todays lecture is being...

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.

Climate change happens

Climate change happens

Rapid variationYounger Dryas

Chicken or the egg?

Man made climate change is real – but local

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 hockey stick

Sea Levels are rising … (IPCC TS2001)

Sea level rise

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.