Tipping points - Lecture 7 (biosphere tipping points)

what % of land could experience significant biome shifts

15%

how does the amazon generate its own rainfall

generates half of its own rainfall by recycling moisture 5-6 times as airmasses move from the adlantic ocross to the west

what is transpiration in the amazon

water vapor is released durong photosynthesis

what is self-amplified forest loss

how the amazon recyceles moisture and rainfall

how to tell wether the water is from oceans or evaporation

• Moisture that evaporates from the ocean tends to be isotopically lighter than water vapor released into the atmosphere by plants. That's because during evaporation, water molecules containing deuterium, a heavy isotope of hydrogen made of one proton and one neutron, get left behind in the ocean. By contrast, in transpiration, plants simply suck water out of the soil and push it into the air without changing its isotopic composition

how do tree-induced rain clouds have effects on the weather

As those clouds release rain, they warm the atmosphere, causing air to rise and triggering circulation. This circulation is large enough that it triggers the shift in wind patterns that will bring in more moisture from the ocean.

what is happening in peru

spread of small - scale cattle ranching, gold mining, road building, and the establishment of oil palm plantations have all helped push annual clearing rates to some of the highest level in that country since the early 2000s.

what are deforestation tactics

Increase of clearing during the rainy season, when clouds obstruct most satellite views of the rainforest. More radar data to be used in forest monitoring systems because radar can see through clouds.

what are the impacts of deforestation

• endagerment or extinction of many rare species including jaguars

• pressuring indigneous communities who depend on forest

How much deforestation would be required to cause the cycle to degrade to the point of being unable to support rain forest ecosystems?

Where might the tipping point be for deforestationgenerated degradation of the hydrological cycle?

The very first model to examine this question showed that at about 40% deforestation, central, southern and eastern Amazonia would experience diminished rainfall and a lengthier dry season, predicting a shift to savanna vegetation to the east.

Other studies suggest negative synergies between deforestation, climate change, and widespread use of fire indicate a tipping point for the Amazon system to flip to non-forest ecosystems in eastern, southern and central Amazonia at 20-25% deforestation

The severity of the droughts of 2005, 2010 and 2015-16 could well represent the first flickers of this ecological tipping point. These events, together with the severe floods of 2009, 2012 (and 2014 over SW Amazonia), suggest that the whole system is oscillating.

how are droughts impacting the forests

drying it out and afffecting the amount of moisture is in the forest. As global temperatures rise, seasonal droughts increase, and part of the rainforest could switch – either to a seasonal forest or savanna state.

what is the total area of boreal forests

1.4 billion hectares or 38% of the global forest area

1/3 is under by permafrost

what is happing to the boreal forests due to increased warming

twice as quickly as the global average. “Increasingly warm summers becoming too hot for the currently dominant tree species, increased vulnerability to disease, decreased reproduction rates and more frequent fires causing significantly higher mortality, all contribute.

• One may think that boreal forests would simply migrate northwards as temperatures rise,

• Climate zones are shifting northwards an order of magnitude faster than the ability of trees to migrate. The boreal forest will expand slightly at its northern edge: woody shrubs are already projected to expand to cover 24–52% of arctic tundra by 2050, resulting in an overall positive feedback effect on climate:

  • - changes in albedo (heat reflection) -

  • increasing amounts of water vapour in the atmosphere

  • expansion of fire into tundra, causing large reductions in soil carbon stock

what is happening in the southern part of the boreal forest zone

climate change may cause closed forest to be replaced by open woodland or scrubland

new vegetation types have lower biomass than those they replace, large amounts of carbon will be released into the atmosphere during such a transition. At the same time the total boreal forest area, and thus its capacity as a carbon sink, will be reduced. This carbon loss is likely to offset any carbon gains from projected expansion of boreal forest into tundra in the north.

what is happening to coral reefs

When water temperatures exceed a certain threshold, corals irreversibly bleach, triggering coral death. Ocean acidification, which is a chemical consequence of global heating, worsens such warming-induced degradation.

Due to their narrow temperature tolerances, some species of corals are currently living at or near their thermal limits

what are the projected increases of corals

Projected increases in sea surface temperature suggest the thermal tolerance of reef-building corals will be exceeded within the next few decades. The IPCC has estimated that between 70% and 90% of tropical and subtropical coral reef will be lost at around 1.5°C above pre-industrial mean temperatures, with near total loss by 2°C

why is macroalgae bad

bquickly takeover dead coral skeletons, potentially preventing them from being recolonised by corals and leaving them in an altered, albeit stable, state. These shifts can be rapid, taking place over months.