GEOG 311-3-3 Environmental Management

NeighbourWoods is a residential planting initiative developed to encourage citizens to help grow and preserve Kelowna’s urban forest. Each year, Kelowna residents can purchase one tree per household for the low price of $40 (plus GST).

The restoration of trees remains among the most effective strategies for climate change mitigation. We mapped the global potential tree coverage to show that 4.4 billion hectares of canopy cover could exist under the current climate. Excluding existing trees and agricultural and urban areas, we found that there is room for an extra 0.9 billion hectares of canopy cover, which could store 205 gigatonnes of carbon in areas that would naturally support woodlands and forests. This highlights global tree restoration as our most effective climate change solution to date. However, climate change will alter this potential tree coverage. We estimate that if we cannot deviate from the current trajectory, the global potential canopy cover may shrink by ~223 million hectares by 2050, with the vast majority of losses occurring in the tropics. Our results highlight the opportunity of climate change mitigation through global tree restoration but also the urgent need for action.

An interview with professor Tom Crowther of ETH Zurich, one of the authors of a Science article suggesting that re-forestation may be the most effective action countries can take to combat climate change. Planting trees on treeless, non-agricultural, non-urban land at the scale the group suggests could bring carbon pollution down to a level not seen in a century. [ABSTRACT FROM AUTHOR]

Nordhaus' DICE model is used to investigate the economics of planting trees on 900 million ha of lands that can be reforested or afforested, as proposed by a number of researchers. By looking at the most optimistic restoration case, a large terrestrial sink can reduce projected future temperatures by more than 30%, with accompanying smaller marginal damages. It also turns out that optimal levels of industrial emissions increase, thereby reducing the beneficial temperature response of the forestry investment. While the results appear optimistic, the forestry project takes too long to have an impact if climate change is considered to be an urgent problem. Based on the analysis, one can conclude that the forestry tool needs to be implemented immediately or not at all.

Primary forest is natural forest of any age. Primary forest includes forest disturbed naturally, for example by wildfire, insects or wind, but excludes forest that has been degraded by logging, roads, or other industrial human activities.

Simply planting trees will not necessarily slow down climate change, an analysis of Europe's vegetation history shows. Although the continent's forests have expanded by 10% since 1750, timber harvesting and shifts to more commercially valuable tree species have resulted in a net release of carbon to the atmosphere.

Afforestation and forest management are considered to be key instruments in mitigating climate change. Here we show that since 1750, in spite of considerable afforestation, wood extraction has led to Europe's forests accumulating a carbon debt of 3.1 petagrams of carbon. We found that afforestation is responsible for an increase of 0.12 watts per square meter in the radiative imbalance at the top of the atmosphere, whereas an increase of 0.12 kelvin in summertime atmospheric boundary layer temperature was mainly caused by species conversion. Thus, two and a half centuries of forest management in Europe have not cooled the climate. The political imperative to mitigate climate change through afforestation and forest management therefore risks failure, unless it is recognized that not all forestry contributes to climate change mitigation.

Changes in forest cover affect the local climate by modulating the land-atmosphere fluxes of energy and water. The magnitude of this biophysical effect is still debated in the scientific community and currently ignored in climate treaties. Here we present an observation-driven assessment of the climate impacts of recent forest losses and gains, based on Earth observations of global forest cover and land surface temperatures. Our results show that forest losses amplify the diurnal temperature variation and increase the mean and maximum air temperature, with the largest signal in arid zones, followed by temperate, tropical, and boreal zones. In the decade 2003-2012, variations of forest cover generated a mean biophysical warming on land corresponding to about 18% of the global biogeochemical signal due to CO2 emission from land-use change.