Hugo Beltrami

Chapter 1 Mediterranean climate variability over the last centuries: A review

Publisher Summary This chapter discusses a necessary task for assessing to which degree the industrial period is unusual against the background of pre-industrial climate variability. It is the reconstruction and interpretation of temporal and spatial patterns of climate in earlier centuries. There are distinct differences in the temporal resolution among the various proxies. Some of the proxy records are annually or even higher resolved and hence record year-by-year patterns of climate in past centuries. Several of the temperature reconstructions reveal that the late twentieth century warmth is unprecedented at hemispheric scales and is explained by anthropogenic, greenhouse gas (GHG) forcing. The chapter discusses the availability and potential of long, homogenized instrumental data, documentary, and natural proxies to reconstruct aspects of past climate at local- to regional-scales within the larger Mediterranean area, which includes climate extremes and the incidence of natural disasters. The chapter describes the role of external forcing, including natural and anthropogenic influences, and natural, internal variability in the coupled ocean–atmosphere system at subcontinental scale.

Evidence for recent warming from perturbed geothermal gradients: examples from eastern Canada*

Recent variations of the surface temperature of the Earth can be inferred from borehole temperature measurements. Generalized inversion is used to extract the information from the data; the potential of the method is evaluated. Tests were performed with synthetic data to demonstrate the effectiveness of the inversion to recover the gross features of the surface temperature history even when the data are affected by noise and errors. The tests show that it is possible to reconstruct the long term changes in ground temperature during the past 300 years; the resolution decreases with time, in particular if noise and errors must be filtered. Temperature logs, obtained in eastern Canada, and not suspected of being affected by non-climatic factors, have been inverted. The analysis confirms that eastern Canada has experienced warming by 1 to 2°C over the past 100–200 years. The relationship between air and ground temperatures has been examined. In eastern Canada ground temperature follows air temperature closely in summer but stays well above air temperature in winter. The number of days with snow on the ground correlates with the difference between annual mean ground and air temperature.

Recent warming in eastern Canada inferred from geothermal measurements

Borehole temperature measurements from several sites in eastern Canada were analyzed to determine recent step changes in ground surface temperature. Inversion of the data suggests a warming by 1 to 2°C in the last 100 years for most of the sites analyzed.

Carbon dioxide in soil profiles: Production and temperature dependence

The temperature dependance of soil respiration has most commonly been addressed using surface flux data, despite the fact that surface flux measurements implicate CO 2 transport and storage effects that may preclude robust assessments of the temperature dependence of soil respiration. Here we examine whether soil respiration might be assessed using soil profile CO 2 production inferred from soil CO 2 concentration profiles. Over the 9-month study period, we observed marked similarities in the temperature response of CO 2 production across four study sites of contrasting vegetation cover and land use.

Simulation and inversion of borehole temperature profiles in surrogate climates: Spatial distribution and surface coupling

A heat-conduction forward model driven by ground surface temperature from three 1000-year climate simulations with the state-of-the-art ECHO-g model has been used to simulate underground temperature perturbation profiles. An inversion approach has been applied to reconstruct ground surface temperature histories from the simulated profiles and to compare them with the climate model temperatures. Results support the skill of borehole inversion methods to retrieve long-term temperature trends, and the robustness of using the present-day borehole network for reconstructing SAT variations.

On the relationship between ground temperature histories and meteorological records: a report on the Pomquet station

Abstract An experimental air–ground climate station is operating in Pomquet, Nova Scotia, monitoring meteorological (surface air temperatures at three heights, wind velocity and direction, incoming solar radiation, precipitation, snow depth and relative humidity) and ground thermal variables (soil temperatures at depths of 0, 5, 10, 20, 50 and 100 cm). Readings are taken every 30 s and 5 min averages are stored, in order to characterize the energy exchanges at the air ground interface. Here, I report on the first year of operation. For spring, summer and fall, we find that soil temperatures track surface air temperatures with amplitude attenuation and phase lag with depth confirming that heat conduction adequately describe the soil thermal field at the Pomquet site. For winter conditions, we find that heat transfer is dominated by latent heat released during soil freezing and to a lesser extent by the insulating affect of snow cover. A numerical model of heat conduction was used in order to estimate the magnitude of the heat released by freezing during the winter months. I also show that there is an inverse correlation for the difference between soil (100 cm) and air temperatures and the incoming solar radiation at the site.

An examination of short- and long-term air-ground temperature coupling

Data from two experimental air–ground climate stations operating at field and wooded sites in Nova Scotia (Canada), monitoring meteorological and ground thermal variables, were examined along with longer-term records of air and soil temperature in order to clarify the energy exchanges at the air–ground interface. A simple, first-order approximation, multilayer numerical model of heat conduction was used to assess whether soil temperatures track air temperature variations at each location. Data indicate that in winter, when soil freezing occurs, the heat transfer regime between the lower atmosphere and the ground is dominated by latent heat released at field and wooded sites. In spring and summer, the ground thermal response at the field site is driven by direct solar radiation heating rather than by conduction. Results from a numerical model indicate that during a frost-free period of 290 days in spring, summer and fall, the soil thermal regime in the forest can be modelled using surface air temperature data as the driver at the upper boundary and assuming a purely conduction dominated scenario, such that at these short time scales, the forest floor and lower atmosphere appear to be coupled. Longer-term records (f30 years) from selected climatological stations across Canada indicate that soil–air temperature differences appear to be temporally variable at all locations examined. If this variation is common and persistent, then the coupling between air and ground temperatures may not be as straight forward as previously though at some locations. D 2003 Elsevier B.V. All rights reserved.

Ground temperature histories in eastern and central Canada from geothermal measurements: evidence of climatic change

Abstract Inverse and direct methods have been used to analyze a large number of borehole temperature logs in order to infer past climatic changes. Results indicate a warming of 1–2°C in eastern and central Canada during the past 150 years. A period of cooling between 500 and 200 years before present, corresponding to the time of the “Little Ice Age”, has also been identified in the same areas. A regional ground temperature history is estimated for eastern and central Canada from the simultaneous inversion of several temperature logs. The inferred temperature changes appear correlated with the concentration of atmospheric carbon dioxide as reported from a Greenland ice core, and agree with existing meteorological and dendrochronological records for the area.

Ground temperature histories for central and eastern Canada from geothermal measurements: Little Ice Age signature

Deep borehole temperature profiles have been analyzed to determine ground temperature histories in central and eastern Canada. Clear signs of a cold period between 1500 and 1800 A.D., corresponding to the little ice age, have been found. A warming trend after 1800 A.D. was detected throughout eastern and central Canada. Temperature profiles from western Ontario are consistent and were inverted simultaneously to yield a regional ground temperature history. The recent warming appears to be correlated with the increase of atmospheric CO2 reported for a Greenland ice core.

Resolution of ground temperature histories inverted from borehole temperature data

Abstract Inversion methods have been used to determine ground temperature history from borehole temperature data. This paper examines the resolution of an inversion method based on singular value decomposition. The method includes in the constraints the rate of change of subsurface if available. The response of the Earth to a unit pulselike change in surface temperature and the model resolution were calculated to determine the details of ground temperature variations obtainable from geothermal data. The model parameters estimated by the inversion correspond to averages over time intervals of increasing length with time. For a unit impulse temperature change occurring at time t before present, the estimated ground temperature history shows the event “spread” over at least 60% the time of occurrence. In practice, the resolution is not improved by increasing the sampling frequency of the data. Likewise, the simultaneous inversion of the temperature profile and of its time derivative does not significantly improve the resolution. Selection of a particular parametrization may improve resolution of the chosen parameters, but not the actual resolution since the parameters represent longer time averages. Temperature data from the Minchin Lake borehole in western Ontario, which was logged twice over 15 years, have been inverted to illustrate these conclusions.