Speakers
Valérie Masson-Delmotte discussing past changes in temperatures using ice cores.

Valérie Masson-Delmotte discussing past changes in temperatures using ice cores.

Valerie Masson-Delmotte (LSCE, Gif-sur-Yvette, France)

Danny McCarroll (Swansea University, Swansea, Wales)

 

Why is it important to measure and quantify past climate change?

To fully understand the nature of past climate change, it is important to use palaeo datasets to quantify key parameters such as: the rate of change; the magnitude of variation; the degrees of temperature change. This information can help us to develop more accurate predictions of future climate conditions. To do so, we need need to use a range of environmental archives (including marine and ice cores) and proxies (such as pollen and isotopes) at a variety of timescales.

 

What have been the major developments in measuring climate change?

The use of ice cores from the polar ice sheets has been a major advancement in our understanding of past climate change. Ice cores provide a high resolution archive of past climate conditions over timescales of up to 800,000 years. Using air bubbles, dust particles, and water inclusions within the ice we can assess a variety of environmental parameters such as: temperature, atmospheric moisture, and dust concentrations.

 

These proxies can help us to assess climate characteristics at different scales:

  • The isotopic composition of air bubbles indicates global sea level characteristics.
  • Aerosols (such as particulates within the ice) indicate regional atmospheric conditions.
  • The isotopic composition of water inclusions within the ice provides information on local moisture source.

Using these different proxies, we can start to compare climate conditions between the two poles, as well as with other archives of environmental change (such as lake sediment and marine records).

 

There has now been over 60 years of ice core drilling. In the 1950s the first 100 m long cores were taken from Antarctica, Alaska, and Greenland. By 1957-58, depths of up to 300 m were reached in Greenland and Antarctica. By the 1960s, the deep cores at Camp Century and Byrd drilling stations reached 1,000-2,000 m. Continued developments in drilling technology meant that in 2012 the deepest core was obtained from Vostok in Antarctica, to a depth of 3,769 m. During this 60 year history, there have been three major revolutions in the use of ice core records.

 

1950s-1970s

The isotopic composition of water inclusions within the ice was developed as a reliable indicator of surface temperature (the ‘isotope thermometer’ technique). Variations in the thickness of ice layers was also developed as a mechanism for assessing changes in precipitation and surface snow cover.

 

1980s-2000s

The isotope-climate relationships were developed further and this information was incorporated into atmospheric models. The use of high resolution isotopic datasets allowed us to develop more robust reconstructions of past climate change, and use this knowledge to formulate more accurate projections of future climate scenarios.

 

2010-present

Over the last few years, one of the major developments in ice core isotope science has involved the use of 17O as a high accuracy measure of relative humidity at sea level. This has been coupled with the use of deuterium (D) excess as a proxy for moisture source.

 

Danny McCarroll explaining the potential ways in which we can further our understanding of climate change over different time scales

Danny McCarroll explaining the potential ways in which we can further our understanding of climate change over different time scales

What are the major challenges?
  • When looking at the last millennia, the climate signal from Greenland is coherent and well understood, but in Antarctica more work is needed.
  • We need to consider the role of snow metamorphism (the transformation of snow to firn and then ice) in transforming the isotopic signal in snow into the ice core record.
  • There has been some good progress in site selection and drilling capabilities of ice cores. We have also begun to link ice core records to other archives, and need to continue developing this.
  • Understanding the moisture source of snow – so that we can understand its isotopic signals.
  • Using new techniques and technologies to investigate high frequency variability.
  • Assessing Antarctic ice sheet-climate interactions.
  • Developing better forecasting of climate changes – through understanding the drivers of change and potential feedback mechanisms.
  • We need to remember that all models are built for particular purposes, and some processes can be missing. Models need to stop averaging over time and space; they should be tested in situ, and with the season that matches the proxy used.
  • Investigating the importance of orbital scale forcing mechanisms on climate dynamics and establishing the response, sensitivity, and feedback of the Earth system to these external drivers.
  • Exploring internal drivers/mechanisms such as: radiation, greenhouse effect, albedo (ice sheets, sea level, dust, veg).