The IPCC in its 2007 Fourth Assessment Report (AR4) found that global warming is "unequivocal" and is "very likely" caused by human activities. Moreover, the climate system inertia and existing human infrastructure guarantees that further climate change will occur. Accordingly, while mitigation of global warming is essential by reducing greenhouse gas emissions, adaptation to climate change is also essential. How we best do that is a major issue requiring interactions between physical scientists, who provide the best information possible, and social scientists, who are involved in how best society can adapt to the projected changes to minimize impacts, reduce vulnerability, and best use the information to improve decisions. We should adapt to climate change by planning for it and making better predictions of likely outcomes on several time horizons.
Climate Information System
Accordingly, we have argued that an imperative is to build a climate information system. The first step is a more comprehensive analysis and assessment of the current state of the climate system, as well as what has happened recently and an assessment of why. This means making full use of available observations of not just the state of the climate system, but also the forcings [the atmospheric composition (greenhouse gases and aerosols), the sun (across the electromagnetic spectrum (ultraviolet to infrared)), and the land surface (changes in vegetation and its health, changes in land use etc)]. It also means linking the observed changes to the forcings and fully understanding why recent climate anomalies have occurred (such as the role of the recent La Niña). This immediately informs the prospects for reliable predictions. However, we already have a lot of observations and analyses. Some are not processed as quickly as they might be (near real time) and it is only a first step to produce the information base. It is another step entirely to promulgate and dispense this information to decision makers and users through a full climate service that also seeks feedback from and informs users about prospects for new products.
CAS is making important contributions to all key components of a climate information system, including:
- Observations: CAS evaluates observations and promotes their reprocessing and reanalysis into global fields. We advocate improved observations and analysis suitable for climate (satisfying the climate principles that are designed to ensure continuity of record). This especially includes those from space. CAS maintains a data catalog and works to enable access to data and products through the internet via the CAS web pages.
- Analysis: CAS develops analytical and diagnostic techniques to process observations and model data, and facilitates their comparison and evaluation. In part, this is through the development, exploitation and promotion of NCL. Value-added derived products are also developed and archived in the data catalog and new datasets are made available.
- Assimilation: CAS advocates analysis of observations into forms suitable for use in models and to initialize models. Within NCAR this is mainly done by MMM and the DART group in CISL. Assimilation enables reanalysis and model diagnostics that can be compared with observations to evaluate and improve models.
- Attribution: CAS has carried out many studies on mechanisms and modes of variability that have contributed to observed climate anomalies. CAS helps develop capabilities that contribute to an operational attribution activity by pioneering studies and numerical experimentation that might be used in near real time to allow reliable statements to be made not only about what the state of the climate is, but also why it is the way it is. Studies involve the atmosphere and the fully coupled climate system.
- Assessment: CAS uses the information from the analyses and other products to assess the state of the climate. Scientists participate in national (CCSP) and international (IPCC) assessments.
- Prediction and predictability: Predictions are required on multiple time scales and it is evident from the inertia in the climate system and the forcings that there is some predictability associated with the initial state of the climate. CAS studies are carried out to assess the predictability associated with the initial state and thermal inertia, modes of variability, internal mechanisms and coupling among climate system components, and forcings. Evaluations of model strengths and weaknesses, possible improvements, comparisons among models and with observations, and evaluations to score their results in multi-model ensembles are underway. CAS scientists are also involved in regional climate model studies using embedded models (the Nested Regional Climate Model NRCM) in order to adequately represent scales of motion thought to be important.
- Decision making: CAS contributes to how to reduce vulnerability and what the impacts will likely be associated with climate variability and change that in turn contribute to adaptation and risk assessment, such as to ecosystems, water resources, and communities. There is significant interaction between CAS scientists, the public and various stakeholder groups.