7 billion and counting…
The main news hitting the headlines this week is the world’s population surpassing the 7 billion mark. Today is meant to be the big day, and significant attention has been paid on what this could mean for our planet. National Geographic have released a special issue covering how the growing global population is affecting our ecosystems worldwide, from rainforests to mountain glaciers and the the socio-economic consequences of long-term climate change. Accompanying a short video on population growth there is also an Ipod App highlighting the key points with photos taken from around the world and a quiz (the answers are at the bottom and make an interesting read) on demographic statistics.
To calculate how your birth fits into current population growth, the BBC have released an interactive program online. By entering your date of birth, gender, and country of origin you can see how you relate to trends in population expansion.
New Scientist: ‘Climate change what we do and don’t know’.
New Scientist have released a collection of articles stating what we currently know and don’t know about climate change. These articles highlight that substantial improvements have been made in understanding the earth’s climate, but there are still significant uncertainties surrounding the scale and the rate of changes for example in glacial extent and sea level rise.
Climate change and glaciers in southwestern China
An article has been released this week in Environmental Research Letters by Li et al., (2011) studying the long-term change in climate and glaciers around southwestern China. Daily temperature and precipitation measurements were taken between 1961-2008 at 111 stations throughout the region and conclusions indicate temperature patterns over this period are consistent ‘with warming at a statistically significant level’. This increase was more apparent at higher altitudes (>3500m) than at lower altitudes (<1500m) (Table 1, Figure 1), which may account for the rapid glacial retreat observed in mountain regions.
Table 1. Correlation coefficients between trend magnitudes for temperature ( ◦C/a) and precipitation (mm/a) and altitudes (n = 48, when r = ±0.29, P = 0.05). (Note: values for trends significant at the 5% level are set in bold.)
Altitude (m) | Annual | Spring | Summer | Autumn | Winter |
Temperature | 0.36 | 0.25 | 0.46 | 0.36 | 0.33 |
Precipitation | 0.41 | 0.31 | 0.02 | 0.51 | 0.08 |
(Source Lei et al., 2011: 6).
Lei et al., (2011) attributes this greater magnitude of temperature rise in higher altitudes to three main factors:
1. Change in cloud cover;
An increase in low cloud cover at night and a decrease in the total cloud cover and daytime cover had resulted in an increase in temperature as higher levels of insolation are reaching the surface.
2. A positive feedback from snow/ice albedo;
An acceleration in melting would decrease albedo under warming at higher altitudes as the darker ground surface underneath is uncovered. This results in an increased absorption by the surface, causing the temperature to rise causing a further acceleration in melting.
3. Black carbon present in snow.
The ‘darkening’ of the snow increases the absorption of radiation at the surface, causing surface temperature to rise and accelerating glacial melt.
Figure 1. Variation of temperature and precipitation with elevation (Source Lei et al., 2011: 9).
Observations of precipitation variations were less marked, but generally exhibited a weak negative trend between 1961-2008. Lei et al., (2011) attributed this decrease to a strengthening of the Western Pacific Subtropical High and a weakening of the East Asian Monsoon which has become more unreliable and unstable in recent years. This is further supported by ice-cores which in the region which show a decreasing trend in accumulation, especially after 1980.
The article suggests that temperature is a dominant factor controlling glacial extent in southwestern China but also notes significant spatial variability in the response of glaciers to climate change in the region. Potential factors that may account for some of these variations were summarised by Yasunami (2011), of which a few will be discussed in the following weeks:
1. Debris-covered effect (heats the surface when it is thin, but insulates when it is relatively thick, though there is no uniform response.
2. The interaction between glacial lakes and exposed ice parts of glaciers.
3. Atmospheric heating effect over the foothills of the Himalayas due to atmospheric brown clouds (include black carbon, dust and organic matter), resulting in the so called Elevated-Heat Pump (EHP).
4. Snow darkening over non debris-covered regions decreasing snow albedo and accelerating snow melt.
5. Feedbacks.
Reference:
Li, Z., Y. He, W. An, L. Song, W. Zhang, N. Catto, Y. Wang, S. Wang, H. Lui, W. Cao, W. H. Theakstone, S. Wang and J. Du (2011) ‘Climate change and glacier changes in southwestern China during the past several decades’, Environmental Research, 6,4: 1-25.
Yasunami, T.J. (2011) ‘What influences climate and glacier change in southwestern China’, Environmental Research Letters, 6,4: 1-4.
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