Specialty

Paleoclimatology, paleoceanography, radiocarbon research.

Research Interests

The role of the oceans in climate change; cycling of heat, fresh water, and carbon by the oceans; dynamics and consequences of abrupt climate change; radiocarbon dating; 14C as a tracer in the carbon cycle.

Bio

Originally trained in Quaternary and glacial geology, my interests turned to oceanography after noting the profound influence of ocean heat transport on ice sheet growth and retreat in the Arctic. I was amongst the first to show that the timing and speed of changes in the large scale overturning circulation of the oceans matched that predicted by paleo-temperature records from Greenland ice cores and (the then) nascent numerical models of ocean circulation. In the run-up to the 1992 Rio Earth Summit (at which the United Nations Framework Convention on Climate Change was opened for signing) I gave testimony to the U.S. Senate warning that unmitigated warming could lead to changes in the overturning circulation of the northern North Atlantic—a phenomenon now clearly visible in regional air and sea temperatures 25 years later. For the last two decades my work has focused on studies of the ocean’s role in determining Ice Age (natural) CO₂ variations and on the use of ¹⁴C as a tracer in the contemporary carbon cycle and for direct quantification of anthropogenic CO₂ emissions.

News

• A landscape unseen in over 40,000 years (2019)
• One fifth of Los Angeles' CO₂ rises from the urban biosphere (2018)
• Ozone treaty taking a bite out of U.S. greenhouse gas emissions (2017)
• The climate lab that sits empty (2017)
• Humans, not climate change, wiped out Australian megafauna (2017)
• In memoriam: John Trevor Hollin, 1930-2016 (2016)
• When less is more: New study tracks down lingering source of carbon tetrachloride emissions (2016)
• Ancient extinction of giant Australian bird points to humans (2016)
• INSTAAR study shows unprecedented warmth in Arctic (2013)
• New monitoring system clears up murky questions about greenhouse gases (2012)
• New climate study may answer long-standing questions about Little Ice Age (2012)
• Atmospheric CO2 pulses at the end of last ice age originated from the deep ocean (2007)
• A better radiocarbon clock improves understanding of Earth’s carbon cycle and geomagnetic field (2004)
• Increasing nitrogen in soils may signal global changes, CU researchers say (2002)