Klimaänderung. Robert Sausen Deutsches Zentrum für Luft- und Raumfahrt Institut für Physik der Atmosphäre Oberpfaffenhofen

Transcription

1 Klimaänderung Robert Sausen Deutsches Zentrum für Luft- und Raumfahrt Institut für Physik der Atmosphäre Oberpfaffenhofen Vorlesung WS 2017/18 LMU München

2 7. Wolken und Aerosole

3 Contents of IPCC 2013 Working Group I: the Physical Science Basis

4 Contents of IPCC 2013 Working Group I: the Physical Science Basis

5 Statements in the Executive Summary Progress in Understanding (1) Many of the cloudiness and humidity changes simulated by climate models in warmer climates are now understood as responses to large-scale circulation changes that do not appear to depend strongly on sub-grid scale model processes, increasing confidence in these changes. For example, multiple lines of evidence now indicate positive feedback contributions from circulation-driven changes in both the height of high clouds and the latitudinal distribution of clouds (medium to high confidence). However, some aspects of the overall cloud response vary substantially among models, and these appear to depend strongly on sub-grid scale processes in which there is less confidence

6 Overview of forcing and feedback pathways involving greenhouse gases, aerosols and clouds

7 What is "radiative forcing"? (simplified) equilibrium RF = 0 perturbed situation RF > 0 T atmosphere atmosphere soil / ocean soil / ocean

8 Forcing, Response and Feedback RF J 0 T T 0 = 0 J 0 = 0 RF RF J T J F J = RF + J = RF + F T T = 0 J = 0 (RF + F T) = RF ratio of responses: r = T / T 0 = 0 / = 1 / (1 f) feedback factor: f = F 0 feedback: F

9 Randel, CSU, Kinds of feedbacks (1): Albedo feedback

10 Kinds of feedbacks (3): Water vapour feedback As water vapor increases, precipitation and evaporation also increase. Randel, CSU,

11 Randel, CSU, Kinds of feedbacks (3): Lapse-rate feedback

12 What is the "lapse rate?" The "lapse rate" is the rate at which temperature decreases upward. In the future climate, the temperature is predicted to increase throughout the troposphere, but it increases more aloft than near the surface. The lapse rate is, therefore, said to decrease. Warmer air up high can radiate heat away to space more easily than warmer air near the ground. Randel, CSU,

13 Randel, CSU, Kinds of feedbacks (3): Lapse-rate feedback

14 Kinds of feedbacks (4): Cloud feedback(s) Cloud amount Cloud top height Cloud optical properties Randel, CSU,

15 Kinds of feedbacks (4): Low-Cloud Feedback Note: This feedback can be either positive or negative. Randel, CSU,

16 Kinds of feedbacks (4): High-Cloud Feedback Note: This feedback can be either positive or negative. Randel, CSU,

17 Statements in the Executive Summary Progress in Understanding (1) Many of the cloudiness and humidity changes simulated by climate models in warmer climates are now understood as responses to large-scale circulation changes that do not appear to depend strongly on sub-grid scale model processes, increasing confidence in these changes. For example, multiple lines of evidence now indicate positive feedback contributions from circulation-driven changes in both the height of high clouds and the latitudinal distribution of clouds (medium to high confidence). However, some aspects of the overall cloud response vary substantially among models, and these appear to depend strongly on sub-grid scale processes in which there is less confidence. Climate-relevant aerosol processes are better understood, and climate-relevant aerosol properties better observed, than at the time of AR4. Cosmic rays enhance new particle formation in the free troposphere, but the effect on the concentration of cloud condensation nuclei is too weak to have any detectable climatic influence during a solar cycle or over the last century (medium evidence, high agreement)

18 Forcing, Response and Feedback RF J 0 T T 0 = 0 J 0 = 0 RF RF J T J F J = RF + J = RF + F T T = 0 J = 0 (RF + F T) = RF ratio of responses: r = T / T 0 = 0 / = 1 / (1 f) feedback factor: f = F 0 feedback: F

19 Statements in the Executive Summary Progress in Understanding (2) Recent research has clarified the importance of distinguishing forcing (instantaneous change in the radiative budget) and rapid adjustments (which modify the radiative budget indirectly through fast atmospheric and surface changes) from feedbacks (which operate through changes in climate variables that are mediated by a change in surface temperature)

20 Overview of forcing and feedback pathways involving greenhouse gases, aerosols and clouds

21 Radiative forcing (RF) and effective radiative forcing (ERF) estimates

22 Schematic of the new terminology used in AR5 for aerosol radiation and aerosol cloud interactions

23 Statements in the Executive Summary Progress in Understanding (2) Recent research has clarified the importance of distinguishing forcing (instantaneous change in the radiative budget) and rapid adjustments (which modify the radiative budget indirectly through fast atmospheric and surface changes) from feedbacks (which operate through changes in climate variables that are mediated by a change in surface temperature). The quantification of cloud and convective effects in models, and of aerosol cloud interactions, continues to be a challenge. Climate models are incorporating more of the relevant processes than at the time of AR4, but confidence in the representation of these processes remains weak. Precipitation and evaporation are expected to increase on average in a warmer climate, but also undergo global and regional adjustments to carbon dioxide (CO 2 ) and other forcings that differ from their warming responses. Moreover, there is high confidence that, as climate warms, extreme precipitation rates on for example, daily time scales will increase faster than the time average

24 Diverse cloud regimes reflect diverse meteorology

25 Annual mean cloud parameters

26 Cloud cover and vertical velocity

27 Cloud radiative effects and precipitation

28 Statements in the Executive Summary Water Vapour, Cloud and Aerosol Feedbacks The net feedback from water vapour and lapse rate changes combined, as traditionally defined, is extremely likely positive (amplifying global climate changes). The sign of the net radiative feedback due to all cloud types is less certain but likely positive. Uncertainty in the sign and magnitude of the cloud feedback is due primarily to continuing uncertainty in the impact of warming on low clouds. Aerosol climate feedbacks occur mainly through changes in the source strength of natural aerosols or changes in the sink efficiency of natural and anthropogenic aerosols; a limited number of modelling studies have bracketed the feedback parameter within ±0.2 W m 2 o C 1 with low confidence

29 Robust cloud responses to greenhouse warming

30 Atmospheric aerosol and environmental variables and processes influencing aerosol radiation and aerosol cloud interactions

31 Mass concentration (μg m 3) of seven major aerosol components for particles with diameter smaller than 10 μm

32 Spatial distribution of the 550 nm aerosol optical depth (AOD) and the 532 nm aerosol extinction coefficient (km 1 )

33 Schematic depicting the myriad aerosol cloud precipitation related processes occurring within a typical GCM grid box

34 Statements in the Executive Summary Quantification of climate forcings due to aerosols and clouds The ERF due to aerosol radiation interactions that takes rapid adjustments into account (ERF ari ) is assessed to be 0.45 ( 0.95 to +0.05) W m 2. The RF from absorbing aerosol on snow and ice is assessed separately to be (+0.02 to +0.09) W m 2. The total ERF due to aerosols (ERF ari+aci, excluding the effect of absorbing aerosol on snow and ice) is assessed to be 0.9 ( 1.9 to 0.1) W m 2 with medium confidence. Persistent contrails from aviation contribute a RF of ( to +0.03) W m 2 for year 2011, and the combined contrail and contrail-cirrus ERF from aviation is assessed to be (+0.02 to +0.15) W m

35 Annual mean top of the atmosphere radiative forcing due to aerosol radiation interactions (RF ari )

36 Estimates of RF ari, ERF ac i and ERF ari+aci

37 Statements in the Executive Summary Geoengineering Using Solar Radiation Management Methods Theory, model studies and observations suggest that some Solar Radiation Management (SRM) methods, if practicable, could substantially offset a global temperature rise and partially offset some other impacts of global warming, but the compensation for the climate change caused by GHGs would be imprecise (high confidence). Numerous side effects, risks and shortcomings from SRM have been identified

38 8. Anthropogener und natürlicher Strahlungsantrieb