ENVR1150 Climate Change Impacts & Extreme Weather Events PDF

Toward More High-Resolution ENVR1150 [24Sep] Climate Change Impacts & Extreme Weather Events IM, Eun-Soon Department of Civil and Environmental Engineering Division of Environment and Sustainability Review Climate projectio...

Toward More High-Resolution ENVR1150 [24Sep] Climate Change Impacts & Extreme Weather Events IM, Eun-Soon Department of Civil and Environmental Engineering Division of Environment and Sustainability Review Climate projection refers to how the statistics of the climate system will change in response to the boundary conditions such as CO2 concentration. (True or False) Climate model simulations show the different seasonality between the equatorial region and high latitude region, which results from a difference in initial conditions. (True or False) Climate model simulations on decadal and longer time scales depend primarily on boundary conditions such as topography. (True or False) Inadequately prescribed complex terrain could be one reason that explains the limited performance of climate model simulations. (True or False) Greenhouse gas concentration is an important initial condition to determine the accuracy of weather forecast. (True or False) Bridging the spatial scale gap between climate information generated using climate models and various impact models is a central issue for climate change impact assessment studies. (True or False) Downscaling technique can be used to derive fine-scale local climate data from coarse grid climate model simulations. (True or False) Since the concept of weather and climate is quite different, the fundamental principles for numerical models to simulate weather and climate differ significantly. (True or False) Review If a certain climate variable is characterized by a large variability, it is difficult to assess the robust signal in response to enhanced greenhouse gas concentrations compared to the variable with less variability. (True or False) The dominance of model uncertainty for precipitation projections implies the diverse performances of current climate models in capturing the characteristics of precipitation. (True or False) The performance of how reasonably the climate models simulate current climate conditions can be one of the indicators to estimate the reliability of future climate projections. (True or False) The use of multiple models could help us quantify uncertainty in future projections. (True or False) The Concept of Feedback Input Output Forcing Climate System Response Process Anthropogenic forcing : GHGs (CO2) : Land-use change Feedback A feedback occurs when a portion of the output from the climate system process is added to the input and subsequently alters the output. An initial change in a process will tend to either reinforce the process (positive feedback) or weaken the process (negative feedback). Climate feedback is important in the understanding of global warming because feedback processes may amplify or diminish the effect of GHG forcing, so in determining the overall climate sensitivity. Some feedback mechanisms (e.g., cloud-radiation feedback) are still mostly uncertain and greatly controversial. The combined effect of all climate feedback processes is to amplify the climate response to forcing (virtually certain). [IPCC AR6 WG1] Feedback Loops Related to Global Warming Decreases ice/snow Increases evaporation Increasing Increases photosynthesis Decreases T vertical gradient CO2 Increases longwave emission Creates Creates changes changes Slower Faster Global Warming Speeds up Slow down warming warming Amplifying Stabilizing [Adopted from Met Office ] Ice Albedo Feedback |Arctic Warming Amplification Ice (or Snow) – albedo feedback is a positive feedback climate process where a change in the area of snow-covered land alters the albedo. Warming tends to decrease ice cover and hence the albedo, increasing the amount of solar energy absorbed, leading to more warming. The differential rate of seasonal or regional warming can be explained by snow– albedo feedback. For example, it can be seen noticeably more warming in response to the elevation during the winter season. Warmer Surface Less snow or ice → Temperature Decrease in albedo More absorbed solar radiation Arctic Warming | Four Times Faster than Global The observations systematically indicate larger AA than CMIP6 models around the year. The Arctic (66.5∘–90∘N) (dark colours) and globally (light colours) during 1950–2021 derived from the various observational datasets. Temperature anomalies have been calculated relative to the standard 30-year period of 1981–2010. Arctic amplification (AA) is defined as the ratio of Arctic warming to the global-mean warming. Frequency distributions of all possible 43-year AA Arctic has been warming nearly four times faster than the globe. ratios between 1970 and 2040 in (a) CMIP5 and (b) CMIP6. The red line denotes the observed 43-year [Rantanen et al. 2022 | Communications Earth& Environment ] AA ratio, as calculated for 1979–2021. Water Vapor Feedback The water vapor feedback is positive feedback because the initial increase in temperature is reinforced by the additional warming. As the atmosphere warms due to greenhouse gases, its concentration of water vapor increases, further intensifying the greenhouse effect. This in turn causes more warming, which causes an additional increase in water vapor. Based on the Clausius-Clapeyron relationship, the atmospheric moisture-holding capacity increases approximately 7% for each 1 K increases in temperature. Warmer Higher Moisture 35.3 − 26.5 Temperature Holding Capacity 35.3 26.5 × 100 /5 26.5 26.5 − 19.7 × 100 /5 Enhanced 19.7 19.7 Greenhouse Effect Planck Feedback The Planck feedback refers to the increase in longwave emission to space with surface warming due to the Planck blackbody radiation law (warmer temperatures = higher emission). A warming planet emits more infrared radiation, and therefore the increase in radiant energy from the surface would greatly slow the rise in temperature and help to stabilize the climate. The increase in radiant energy from the surface as the planet warms is the negative feedback in the climate system, and greatly lowers the possibility of a runaway greenhouse effect. Cloud-Radiation Feedback ❖ Contrast effects of clouds on climate : Clouds reflect a certain proportion of solar radiation back to space, so reducing total energy available to the earth system. : Clouds act as blankets to longwave radiation from the Earth’s surface, so reducing the heat loss to space by the surface. The dominant effect depends on the cloud temperature (height) and optical properties (thickness). The overall cloud effect of clouds can be either positive or negative. Because of the complexity of the processes, cloud feedback is one of the less well- understood feedbacks, and this uncertainty is largely responsible for the spread of climate sensitivity in the present generation of climate models. Diverse cloud regimes [IPCC AR5 WGI | Fig. 7.4] Model’s Uncertainty in Low-level Cloud Feedback ❖ Importance of low-level cloud feedback Low cloud is capable of particularly strong climate feedback because of its broad coverage. The change in low cloud varies greatly depending on the model, causing most of the overall spread in cloud feedbacks and climate sensitivities among climate models. No compelling theory of low cloud amount has yet emerged. ❖ Difference between low (1.5-3°C) and high (3°C) over sensitivity models under CO2 doubling ➔ Presence of lower-tropospheric convective mixing The vertical mixing accompanying a shallow lower troposphere circulation progressively dries the boundary layer as climate warms. If the layer deepens in a warmer climate, more dry air can be drawn down towards the surface, desiccating the layer and reducing cloud amount. No reality [Sherwood et al. 2014 |Nature] CO2 Positive & Negative Feedbacks ❖ CO2 fertilization feedback [Negative] Higher atmospheric CO2 levels increase plant growth rates, which reduces atmospheric CO2 levels. Higher Atmos Accelerate Plant CO2 Level Growth Faster Removal of CO2 from the air ❖ CO2 – water temperature feedback [Positive] Higher atmospheric CO2 increases ocean temperature, which reduces ocean CO2 update and therefore atmospheric CO2 further increases. Higher Atmos Higher Ocean CO2 Level Temperature [https://gotbooks.miracosta.edu/oceans/chapter7.html] Less Ocean CO2 Uptake Example for Feedback Amplification Loops ❖ Estimation of the amplified warming due to water vapor feedback loop From the Global Energy Balance 1 𝜎𝑇𝑒 4 = 𝑆(1 − 𝛼) 4 For the Earth, 𝑇𝑒 = 𝟐𝟓𝟓, 𝐹𝑠 = 239.7 𝑇𝑒 = 𝟐𝟓𝟔, 𝐹𝑠 = 243.5 Δ1℃ ≈ 3.8 𝑊𝑚−2 It is expected that the increase in temperature would be around 1℃ if the increase in radiative forcing would reach around 3.8 𝑊𝑚−2 , which roughly corresponds to the CO2 doubling. However, IPCC AR5 gives a likely range of 1℃ to 4.5 ℃. It’s due to the amplification of the initial warming due to feedback loops. 0.852 0.224 It is expected that the water vapor feedback loop can amplify 1°C warming by more than 1.8 0.473 1.7°C. [For every degree that the temperature rises, it is well known 3.8 1 that the water vapor feedback cycle will add 1.8 𝑊𝑚−2 to the X0.263 energy imbalance.] Radiative Forcing Temperature Change