2. There may be large uncertainties in the dating of materials used to draw timelines for paleo records.

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1 Limitations of Paleo Data A Discussion: Although paleoclimatic information may be used to construct scenarios representing future climate conditions, there are limitations associated with this approach. The following comments represent some perceptions on the limitations of paleo-data as described in a recent Intergovernmental Panel on Climate Change (IPCC) report entitled Guidelines on the use of Scenario Data for Climate Impact and Adaptation Assessment (1999). These limitations were presented to participants at the paleo-workshop and their responses are presented herein. Participants were organised into three groups for this exercise, representing i) long-term Holocene records, ii) paleo-lacustrine and paleomarine records, and iii) high-resolution records from tree-rings and ice-cores. 1. Past Changes in climate are unlikely to have been caused by increasing GHG concentrations. Different boundary conditions mean that we cannot be confident that the characteristics (e.g. Spatial temperatures and ppt patterns) of a warmer GHG induced future climate will resemble those of a past climate which was also warmer. i) Largely disagree that paleo-data is not applicable. Former warm intervals represent partial analogues as to how physical and biologicla systems respond. An example would be the impact of permafrost warming on permafrost we are not so much concerned about the driver of change rather, the impact that this change will have. ii) Boundary conditions are set by expectations and know variance. The only way to define the variance is via paleo-climate records. It is also the only information on the frequency and occurrence of extremes (and/or state change). iii) The things that are changing are temperature and precipitation patterns themselves -- those are what are driving changes. Need an example of what CO2 will do to global circulation. It is probably true that CO2 levels will have unknown influences on tree-ring growth. 2. There may be large uncertainties in the dating of materials used to draw timelines for paleo records. i) Agreed for older periods older than the Last Glacial Maximum and beyond the limit of radiocarbon dating. But otherwise current radio carbon dating has an accuracy of +/- 50 years. High resolution floating (ie relative) chronologies are not affected significantly by large dating uncertainties.. ii) We accept that uncertainties exist, however, we know the main sources and are moving to quantify the effects of the errors. All approaches have large

2 uncertainties and other uncertainties exist as well (for example, spatial variation and inter-indicator differences). All sources of variance need to be addressed. Iii) With respect to tree-rings there can be absolute certainties in chronologies. There may be delays in the response of trees to environmental forcings, but these are short. Other proxy methods have some uncertainties, but they are negligible. The errors are just bigger forms of noise. It is best to have a large spatial coverage. 3. Paleo-reconstructions are generally not geographically comprehensive. i) Agreed, you can never have too much data. However, at a certain level it is quite conceivable to make regional to continental scale synthesis. Syntheses and network analyses are relatively new and not easily discoverable and effort is needed to make the data available. However, it should be done and should be made more obvious to users. ii) All records suffer from geographic problems (e.g. ice cores, model resolution). iii) GCM's have some constraints on spatial scale as well. Similarly, the current network of climate stations in Canada is not geographically comprehensive. The difficulty with the perception that GCMs have good coverage is that all of the numbers are modelled. True climatic parameters are data driven, and temperature and precipitation data can be derived and interpolated regionally. 4. Only mean temperature and precipitation information is available, thus limiting the use of these data in climate change scenarios. i) We agree, many reconstructions are interpreted in terms of mean temperature, and precipitations parameters (either annual or seasonal) and many use paleoecological data and what was known about the climate (temp., precip., nutrients) of the their time. However, most modern ecological preferences (eg treeline, mollusc larvae,etc) are understood in terms of general mean climatic parameters. ii) We agree there is a need to produce ultra high-resolution (seasonal). However, mean temperature and precipitation are the primary controls of ecosystem development, and are therefore key variables. iii) The information is expressed on a species by species basis. The data may be limited to these parameters, but that is data that is most needed. Temperature and precipitation data are derived from the lowest common denominator of the parameters that we use to calibrate the systems. We can get extreme information from these as well, that can be applied to all time-scales, dependent upon the

3 proxy that is used. Caution should be taken on the definition of the mean (annual?) values, as proxy tree-ring records may provide growth-year (July-to- June) means as opposed to calendric (Jan-to-Dec) means. Additional comments) Windiness can be expressed by aerosols in ice core reocrds. Sea salt can be used as an expression of open water. There is much more to proxy records than just temperature and precipitation reconstructions. There have been reconstructions of pressure, atmospheric circulation, etc. 5. Generally, only details of the average and then only seasonal, conditions prevailing in the past can be determined from the reconstructions, only rarely is reliable information available on climate variability or on the frequency of extreme events. i) The strength in the stratigraphic record for geological sequences is that it is best used for extreme events, as they are typically best preserved. Long term records can reproduce extreme events and are best used to capture the variability. Archaeological records give us shifts in culture, which can be caused by large shifts in climate. ii) This criticism is incorrect. The variance measured depends on the question asked. Are we missing weekly events? The resolution needs to be driven by the questions asked far enough in advance. iii) Higher resolution records are site specific. They do exist on that resolution, but are hard to make as a national network. It depends on the time-scale of variability that you are really interested in, especially in terms of extreme events. 6. The reconstructed climate is, in many cases, a steady-state or equilibrium climate, with respect to long term processes of vegetation response to climate, and thus may be quite different in character in character to the transient climate changes anticipated during the 21 st century i) Disagree to some degree equilibrium climates have been sought in past records, and we can then determine the rates of change. At tendency of the traditional way is to average changes with periods of similarity (e.g. pollen zones, pollen boundaries). Data could be shown differently to better show confidence limits. ii) If the comment pertains to the fact that the rate of change in the future is greater than the rate of change in the past, then many paleoecological records disagree. Paleoclimate records are replete with discontinuous changes, whereas

4 others are complacent. Probably both exsist, as there is a regionality of climate, and you may remove the variance that you are interested in. It is a matter or perception -- high resolutions it is hard to come up with a steady state. iii) Climate is continually variable in time and space and the proxy records shows that it is transient Additional comments) We look at intervals, strata, pollen, etc which may imply boundaries. There is a time-scale problem, dealing with 1000, easier to see a homogeneous climate. There are lots of sudden catastrophic climate changes since the Last Glacial Maximum that usually provide stimulus for the modellers. Similarly, proxy records can integrate well with models such for such things as air mass movements. Whatever the forcing is, that is what has moved e.g. jet stream. As well, researchers studying changes in solar output, vulcanicity are looking for global explanations. 7. The more reliable paleoclimate reconstructions tend to indicate climate changes which lie at the low end of the range of anticipated future climate warming; derived temporal analogue scenarios may thus not represent th range of future conditions. i) Reconstructions look at the low end of warming, especially with respects to modelled temperature change in the Canadian arctic. It may have been +3 C warmer in the mid Holocene, versus GCM projections of +7 C, however the last interglacial was similar to the projected warming. ii) Variability is found in the records. Averaging of paleorecords over global scales will act as a filter to remove variation. We recommend retaining the variance until global synthesis is needed. Adaptation will be on a regional scale and could go through a threshold. iii) If you reconstruct the last 1000 years you have the coolest period in last years, as well as some of the warmest, and thus have a range that may be experienced during warming. It may not be as extreme as +4 to +5 C, but that is not the major problem. It should be understood that, in reaching more extreme temperatures we must first pass through the range of temperatures that have been experienced, and for which we can provide information on the environmental responses. 8. The older the paleoclimate information, the less confidence there is in its reliability and the less there are available.

5 i) Generally we agree, but not in all cases. ii) Old data can be reinterpreted, filtered or rejected. If old means early Holocene then there is ample evidence of high-resolution potential. Even with chronological errors, we can still use records to define changes in ecosystem state and variability. iii) The problem is that high resolution can be available, but less generally available because it is less preserved and harder to find.