Climate Change 1. - The Big Picture

Being perfectly honest, this is really just an overview; were I to address every impact that climate change has had upon birds, I would be here for a long, long time. Whilst I can and will focus on the finer points in my future posts, here I simply aim to provide a stepping stone. The topic of Climate Change is a long debated one, and the effect that our activities have had upon the climate is one of the reasons why many believe we're entering a new geological time; the Anthropocene.

What is Climate Change, and how do we know it is happening?
In short, Climate Change is a large-scale, global change in patterns of weather and temperature trends over time. As a result of shifting climate zone boundaries, climate change also results in a shift of biodiversity over time.

Athabasca Glacier in Canada is just one of the world's many retreating mountain glaciers that make it hard to deny that our planet is has been warming over the last century - by Maggie T on Flickr

Climate Change can be natural; the earth has experienced both cool periods where ice has been present over the poles, and warmer ice-free periods. Whilst the exact mechanisms for natural climate change are not fully understood, it is believed changes in the earth's orbit (Milankovitch Cycles) (British Geological Society) (Wikipedia, 2013) play a large role. This sort of climate change, however, takes place over thousands of years. Since the beginning of the 20th century global temperature has risen 0.8°C (1.4°F) (UK MetOffice) (US EPA) (Koronowski, 2013). This rapid change is above and beyond natural climate change (IPCC, 2007) and has been attributed to human activities; primarily an increase in atmospheric CO2 (from 280ppm before the industrial revolution (IPCC, 2007) to the present value of over 390ppm)(CO2 Now) through the burning of fossil fuels.

This rise in temperature has in turn caused a shift in global precipitation pattens (US EPA). Whilst there has been increased rain observed in the northern hemispheres mid-latitudes, other areas of the globe have suffered increasing drought  (UK MetOffice). Climate change has also brought with it a rapid retreat in mountain glaciers (Oerlemans et al, 1998) (Kaser et al, 2003) , a decline in sea ice and continental ice sheets, and a rise in sea level (Rockström et al, 2011).

Threatened by climate change and stronger, more frequent El Niño cycles; the critically endangered Waved Albatross (Phoebastria irrorata), a migratory sea-bird who's population is believed to have declined by up to 19% in the past 84 years (BirdLife, 2013) - image by Victor Burolla on Flickr

How does climate change impact upon birds?
There is compelling evidence that Climate Change has had a large impact on the behaviour, breeding patterns, breeding ranges (Araújo et al, 2005) and migration patterns of birds (Nature Canada). Earlier springs in northern hemisphere have been associated with an earlier arrival and breeding of birds, and in turn an earlier autumn and winter migration of juveniles (Crick, 2004).

For those birds that don't migrate to warmer climates, the harsher, colder winters may pose the threat of starvation and freezing as they require an increased energy expenditure for birds to keep warm (Crick, 2004). In turn, this could impact breeding success.

Other threats posed to birds, both migratory and non-migratory, include the loss of habitat and food (National Geographic, 2013). Whilst some areas of the world are becoming dryer and suffering from drought, other areas are becoming more 'hospitable'; in Alaska trees are now appearing on the formerly tree-less tundra, and deciduous trees are beginning to replace mountain conifers (O'Hara, 2011) . Whole ecosystems are changing rapidly, and populations of birds unable to adapt to these changes may decline rapidly.