The Working Group I contribution to the IPCC Fifth Assessment Report (AR5) addressed the most recent physical science of climate change and provides new scientific evidence, drawing on more extensive observations, greater understanding of climate processes and feedbacks, improved climate models, and a wider range of climate change projections. A large body of evidence supports the conclusion that human activity is the primary driver of recent warming. This evidence has accumulated over several decades, and from hundreds of studies. The first line of evidence is our basic physical understanding of how greenhouse gases trap heat, how the climate system responds to increases in greenhouse gases, and how other human and natural factors influence climate. The second line of evidence is from indirect estimates of climate changes over the last 1,000 to 2,000 years.
The evidence provided by the existing data from complex science is key to addressing the development impacts and the water security implications of climate change. The presence of scientific evidence on the status and extent of climate change impacts on ecosystems, hydrological cycle and human development is a major pillar to prepare for appropriate development responses through the introduction of relevant adaptation and mitigation strategies (see Sub-theme 2: Development Impact). Resources in this section address the wider challenge of interpreting and using climate data in order to plan the development of water resources more effectively.
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