We assess the co-evolutionary dynamics of the Earth's carbon cycle and societal interventions through terrestrial carbon dioxide removal (tCDR) with a conceptual model in a planetary boundary context. The focus on one planetary boundary alone may lead to navigating the Earth system out of the safe operating space due to transgression of other boundaries. The success of tCDR depends on the degree of anticipation of climate change, the potential tCDR rate and the underlying emission pathway.
Veronika Eyring, Peter J. Gleckler, Christoph Heinze, Ronald J. Stouffer, Karl E. Taylor, V. Balaji, Eric Guilyardi, Sylvie Joussaume, Stephan Kindermann, Bryan N. Lawrence, Gerald A. Meehl, Mattia Righi, and Dean N. Williams
We argue that the CMIP community has reached a critical juncture at which many baseline aspects of model evaluation need to be performed much more efficiently to enable a systematic and rapid performance assessment of the large number of models participating in CMIP, and we announce our intention to implement such a system for CMIP6. At the same time, continuous scientific research is required to develop innovative metrics and diagnostics that help narrowing the spread in climate projections.
We describe ESCIMO, a system dynamics simulation model which is designed to make it simple to estimate the effects of possible human interventions to influence the global surface temperature. ESCIMO consists of sectors that track global carbon flows, global energy flows and global albedo change. One conclusion is that human interventions that cost less than 1 % of world GDP are at most able to lower the temperature rise in 2050 by up to 0.5 °C and in 2100 by up to 1.0 °C.
Seasonal predictions have been challenging for mid-latitude regions such as Europe, and we suspect that one reason may be due to subjective choices in how the forecast models are configured. We tested how (1) the inclusion and omission of the representation of the stratosphere affect the predictions and (2) the degree of detail in the sea-ice description. The test was carried out with a set of simulations (experiments) using a technique known as "factorial regression".
We simulated effects of irrigation on climate with the NASA GISS global climate model. Present-day irrigation levels affected air pressures and temperatures even in non-irrigated land and ocean areas. The simulated effect was bigger and more widespread when ocean temperatures in the climate model could change, rather than being fixed. We suggest that expanding irrigation may affect global climate more than previously believed.
The Atlantic Meridional Overturning Circulation (AMOC) is an important oceanic circulation system which transports large amounts of heat from the tropics to the north. This circulation is strengthened when less solar irradiance reaches the Earth, e.g. due to reduced solar activity or geoengineering techniques. In climate models, however, this response is overestimated when chemistry–climate interactions and the following shift in the atmospheric circulation systems are not considered.
The development of global cropland in the future depends on how many people there will be, how much meat and milk we will eat, how much food we will waste and how well farms will be managed. Uncertainties in these factors mean that global cropland could decrease from today's 1500 Mha to only 893 Mha in 2100, which would free land for biofuel production. However, if population rises towards 12 billion and global yields remain low, global cropland could also increase up to 2380 Mha in 2100.
We compare simulated with observed forests to constrain uncertain input parameters of the land surface component of a climate model.
We find that the model is unlikely to be able to simulate the Amazon and other major forests simultaneously at any one parameter set, suggesting a bias in the model's representation of the Amazon.
We find we cannot constrain parameters individually, but we can rule out large areas of joint parameter space.
The ocean is an important vehicle for redistributing Earth's heat from the tropics to high latitudes. We present a conceptual global climate model, with a focus on the coupling between oceanic heat transport and sea ice cover. We use this model to study the role of heat exchange between the ocean and ice components on the global climate system, including investigating the initiation of a global ice-covered climate ("Snowball Earth"), as well as the reversibility of the loss of polar ice caps.
Amazonia is heavily impacted by climate change and deforestation. During annual flooding terrigenous material is imported to the river, converted and finally exported to the ocean or the atmosphere. Changes in the vegetation alter therefore riverine carbon dynamics. Our results show that due to deforestation organic carbon amount will strongly decrease both in the river and exported to the ocean, while inorganic carbon amounts will increase, in the river as well as exported to the atmosphere.
Conflicts over land and water resources between livestock herders and farmers are common in the Sahelian region of Africa. In this paper we show that improved information on weather, grazing areas, and water resources may reduce the level of conflict if communicated in such a way so that not too many livestock herds go to the same areas. However, if this information is not accompanied by information on herd crowding and potential conflict areas, it may lead to more conflict.
This research is about climate change adaptation. It demonstrates how adaptation to climate change can avoid social tensions if done in a sustainable way. Evidence is drawn from Malawi in southern Africa.