ENSC 425/625 Chapter 2UNBC1 Chapter 2 Systems approach Objectives: Couplings & Feedback loops Equilibrium states Perturbations & Forcings CO 2 -temp.-photosyn. feedback system

UNBC2 Blanket T Body T (a) Positive coupling (b) Negative coupling Body T incr. => blanket T decr. Body T Blanket T Body TBlanket T (c) Negative feedback loop (–)

UNBC3 Incorrect setup A’s body TA’s blanket T B’s blanket T A’s body T B’s body T A’s blanket T B’s blanket T Correct setup (–) B’s body T (+)

UNBC4 Is this a positive or negative feedback loop? A HE DBC GF

UNBC5 t t

6 Exceptions about positive feedbacks Positive feedback can => stable equil. if state of one component depends only on the present state of the other component Child’s noise level parent’s anger level

UNBC7 If both parent’s & child’s response are strong => unstable equil. Child’s noise level parent’s anger level

UNBC8 Equilibrium states Correct elec. blanket setup with negative feedback loop => equilibrium state. Stable eq. state Stable eq. state Stable eq. state

UNBC9 Unstable equilibrium states System rarely stays at an unstable equil. state for long.

UNBC10 Perturbations & forcings Perturbation = temporary disturbance of system. E.g. volcanic eruption => aerosol, but effects disappear in 3 yrs. Forcing = more persistent disturbance of system. E.g. Gradual incr. in sun’s output. Gradual incr. in atm. CO 2.

UNBC11 The average climate response to the five largest volcanoes of the last 120 years.

UNBC12 Climate sensitivity: The sensitivity of the climate systems to a forcing is commonly expressed in terms of the global mean temperature changes that would be expected after a time sufficiently long for both the atmosphere and ocean to come to equilibrium with the change in climate forcing. An important factor of climate sensitivity is feedback of components of the climate system. An example: if CO2 concentration doubles (forcing 4w/m^2), the temperature will increase 1.25C if no feedback. However, the situation is very complicated due to feedbacks. For example, CO2 up => T up => ice melting => surface color changes => more sun lights absorbed => T up…. feedbacks cause uncertainty in climate changes..

UNBC13 Feedbacks

UNBC14 Feedbacks

UNBC15 CO 2 -temp.-photosyn. feedback system Atm. CO 2 Photosynthesis (–) T 6CO 2 +6H 2 O -> C 6 H 12 O 6 + 6O 2

UNBC16 Water Vapor Feedback

UNBC17 Ice-Albedo Feedback warming Decreased snow and ice; less reflectivity More solar radiation absorbed at surface

UNBC18 Initial Change Climate warming Increased clouds Greater reflected radiation Reduced Warming Cloud Radiative Feedbacks Uncertain

UNBC19 FEEDBACKS INVOLVED IN GLOBAL WARMING

UNBC20 CLIMATE SENSITIVITY

UNBC21 The ‘commitment’ to future warming CLIMATE SENSITIVITY

UNBC22 Uncertainty in Climate Change Study Scenario uncertainty --- due to uncertainty of future emissions of GHGs and other forcing agents; Model uncertainty --- associated with climate models; Natural variability --- Stochastic and Nonlinear problem; Initial condition uncertainty and forcing and boundary – the limitation of observation data and assimilation technique

UNBC Representative Concentration Pathways (RCPs) The four RCPs --- RCP2.6, RCP4.5, RCP6, and RCP8.5 a possible range of radiative forcing values in the year 2100radiative forcing relative to pre-industrial values (+2.6, +4.5, +6.0, and +8.5 W/m 2, respectively). RCP 2.6 assumes that global annual GHG emissions peak between , with emissions declining substantially thereafter. Emissions in RCP 4.5 peak around 2040, then decline. In RCP 6, emissions peak around 2080, then decline. In RCP 8.5, emissions continue to rise throughout the 21st century. 23

UNBC24

UNBC25

UNBC26

UNBC As observational records lengthen and models improve, researchers should be able, within the limitations of the range of natural variability, to narrow that range in probable temperature in the next few decades. It is also possible to use information about the current state of the oceans and cryosphere to produce better projections up to a few years ahead. 27