In this context, a combination of newly available early observational data and large ensembles of climate model runs now offers an exceptional opportunity to make a step change in our understanding of the nature and drivers of climate variability and change on the societally-relevant timescales of decades to centuries. A comprehensive view of climate change over this critical period can shed light on the causes of the enigmatic early 20th century warming (Broennimann, 2009), and can resolve the controversy if the variability in the 20 century above the trend is externally driven, or an expression of climate variability (see, e.g. DelSole et al., 2010, Booth et al., 2010). Since the climate system shows variability on all timescales (Hasselmann, 1976), the context of the past 200 years provides a more comprehensive understanding of climate variability. TITAN comprehensively analyzes the observed evolution of climate over the 19th and early 20th century period continuously, using new or significantly updated observational datasets in order to learn about the climate system’s response to forcing across multiple key climate variables and timescales.
TITAN uses understanding of climate dynamics and climate modelling to determine the causes of and contributors to the observed climate evolution. Specifically, the project determines the causes of early Anthropocene warming, what this period can teach us about the nature of internal climate variability, and finally what we can learn from this period about sensitivity of the climate system to external forcing and long-term warming from forcing by addressing the following research questions:
- i) What were the roles of external influences on climate evolution during the early Anthropocene?
- ii) What caused the early 20th century warming?
- iii) What role did circulation and greenhouse gas increases play in temperature extremes observed over the early 20th century, and what can we learn from the record?
- iv) What is the sensitivity of precipitation change and sea ice retreat to warming?
- v) What can we learn about internal variability within the climate system from the longer time horizon?
- vi) What is the transient sensitivity of the climate system to an evolving greenhouse gas signal (transient climate response)?