Let's talk climate change

In between talking about billions and millions of years ago, I woud like to remind you that on Monday, December 1st the UN Climate Change Conference will begin in Lima, Peru!  

Let the games begin... #COP20 in Lima :-) pic.twitter.com/W8GiSRYRpj

— #COP20 Lima (@LimaCop20) November 28, 2014

As we have seen, our climate has changed before for different reasons, ranging from tiny microorganisms to huge continents, but generally changes have taken a very long time - thousands or millions of years. Today we are seeing an accelerated climate change, in a very short timescale.

In its latest report the IPCC said:

"Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems."

So, it is also up to us to make the necessary changes to try to mitigate the effects as much as possible. This meeting will be important leading up to Paris 2015, and will mark the trend of where we are heading to in the future.

If you want to follow the action, http://newsroom.unfccc.int/lima/ is a good place to start. Oh, and of course there is an app!
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A frozen planet - II

Planet vitals:

- Average temperature: -20 to -50°C

- Pack ice thickness: 500-1500 m
(Kirschvink, et al., 2000)

Source: BBC

How did the Earth fall into such extreme conditions?

First of all, the young Sun was weaker than in the present day (Tziperman et al., 2011; Young, 2012). Perhaps the only reason the Earth was not under permanent icehouse conditions in the past was the high concentration of greenhouse gases (mainly CO2 and CH4) in the atmosphere. This means that with a reduction in greenhouse gases, the Earth would cool down (Young, 2012 and Tang and Chen, 2013).

CH4 levels fell with the rise of oxygen during the Great Oxidation Event, eliminating one of the greenhouse gases. CO2 reduction was also related with this event, since microorganisms would consume it during photosynthesis (Tang and Chen, 2013). However, weathering is also an important mechanism to drawdown CO2. This is where the supercontinents come in. Young (2012) notes that the Snowball events at the beginning and end of the Proterozoic coincided with the presence of supercontinents. These are very thick and rise higher with respect to sea level than smaller continents, exposing more surface subject to subaerial weathering, so more CO2 can be "buried", effectively reducing atmospheric CO2. Fig. A is a simplified diagram that shows the conditions that made the Snowball Earth events (marked with red arrows) possible. For the first event there was low solar luminosity and a drop in CO2, caused by increased weathering due to the Kenorland supercontinent. Once it broke up, the CO2 drawdown was reduced, but maintained a downward trend (the atmospheric O2 was still rising). Solar luminosity also progressively increased, preventing icehouse conditions despite the lowering CO2. However, once Rodinia was formed, the CO2 weathering increased once again, breaking the balance and plunging the Earth into another glaciation.

Fig. A: Relation between glaciations and supercontinental cycle. Young, 2012

Once the ice began to expand across the planet, there was no stopping it; a runaway ice-albedo effect would be triggered when sea ice crossed between 30° to 40° latitude, causing the whole planet to be covered in ice (Tziperman et al., 2011).

How did it end?

It seems like there is no escape. With the runaway ice-albedo effect, the cooling effect is reinforced endlessly. However, as shown in fig. B, weathering is prevented by the ice cover, allowing CO2 levels to build up again, warming the planet and allowing the ice to melt (Young, 2012). Volcanoes would be the source of CO2 (Hoffman et al., 2002) and Kirschvink et al. (2000) estimated it would take roughly 35 million years to end a Snowball event.

Fig. B: Feedback loop causing alternation between icehouse and greenhouse conditions. Young, 2012.

A frozen planet

After the Archaean-Proterozoic transition, where we left off, the Earth went through severe glaciations that would put the last ice ages to shame. These glaciations lasted from 100 to 200 million years at the beginning and the end of the Proterozoic (Hoffman, 2002). The extent of these glaciations is still debated, with some arguing for Snowball Earth events (Hoffman, 2002), while others suggest the evidence is inconclusive for such widespread events (Young, 2012).

The Huronian glaciations occurred at the beginning of the Proterozoic (2.45-2.22 billion years ago), with at least 3 being identified (Young, 2012). The Sturtian (715 million years ago) and Marinoan (635 million years ago) glaciations occurred at the end of the Proterozoic. 

Fig. A: Current location of Neoproterozoic glacial deposits, and
their estimated original latitudes. Hoffman, 2002

The evidence for these events is found spread around the modern day continents, mainly in the form of glacial deposits, like ice rafted debris. By estimating their original latitudes (figures A and B), it was found that many of these glacial features were formed near the equator (Hoffman, 2002), leading to the idea of frozen world, or Snowball Earth.

Fig. B: Location of Sturtian glacial deposits on the
supercontinent Rodinia. Young, 2012

However, as mentioned before, the extent of these glaciations is not yet clear. A ‘Slushball Earth’ scenario, with open water, is an alternative. Among the arguments against a Snowball Earth (Young, 2012) is that without open water, the hydrological cycle would basically “shut down” and additionally there is evidence for glacial advance and retreat cycles. Another important consideration is how or where microorganisms could have survived in a completely frozen world - photosynthetic organisms had already evolved as discussed previously. Hoffman (2002) argues a weak hydrological cycle would be present and enough for snow to accumulate slowly, eventually allowing for glaciers to flow. Regarding the microorganisms, he says that there were many places where they could survive, like transient meltwater ponds or hot springs around volcanic islands. He argues that microorganisms did not only survive, but benefited from these harsh conditions, since it was only after the Neoproterozoic glaciations that there was an increase in their diversity, and the appearance of the first macrofossils came soon after.

Fig. C: Macrofossil from the Edicaran period (635-542 million years ago). Source: Wikipedia 

In the next post we will explore the possible causes that led to these extensive glaciations and why they occurred so long ago!  

Vulnerability

Along with the regular posts, I will be posting shorter* ones about climate change today. Let's start with vulnerability!

A few days ago the UNEP tweeted an interesting map of a ranking of countries by vulnerability.

This map compares 3 lists of countries ranked by #climatechange vulnerability. Surprised? http://t.co/TmY5EusCti pic.twitter.com/B4Dpj6chLl
— UN Environment (@UNEP) November 1, 2014

Well yes, I was surprised. 

First, because there is a lot of discrepancy between the indices, with several countries appearing among most vulnerable and least vulnerable lists simultaneously. The second thing I noticed is that Peru appears to have no data. 

So let's look at the three indices used to make the map. 

DARA Climate vulnerability monitor

Uses 34 indicators to link the effects of climate change with the economic, ecological and social costs. In the social aspect it includes deaths and number of people affected.

Notre Dame Global Adaptation (GAIN) Index

Their vulnerability score is based on 36 indicators. From the page: "ND-GAIN measures overall vulnerability by considering six life-supporting sectors: food, water, health, ecosystem service, human habitat, and infrastructure."  The total ND GAIN score includes each countries readiness along with the vulnerability.

Germanwatch's Global Climate Risk Index

Uses information of the social and economic effects of extreme weather events that occurred between 1990 and 2009. It does not consider indirect effects or events, such as glacier melting. In the social aspect, it only includes deaths associated with extreme weather events, not number of people affected. It produced two rankings, one for the most affected countries from 1990-2009 and another only for 2009. 

Basically, even though the three indices are related to climate change vulnerability, they are not looking at the same things and are not necessarily comparable. Also, each methodology will have certain limitation based on the data used, so that can explain why the results are not as expected. If something doesn't make sense at first, look at the methodology and data used! This doesn't mean an index is wrong or right, it is just that they have a different goal and will use different data. Each webpage linked has a lot of very interesting information, so check them out.

I must note that I still don't understand why Peru appears as "data non available", since it was analyzed in all three indices (ND GAIN: 71 out of 180 in the vulnerability index; Germanwatch: 47th most affected from 1990-2009 and 51st in 2009; DARA CVM: severely vulnerable). What this shows is that we must all be prepared! Every country will probably be affected in one way or another and it is in our hands NOW to take the necessary measures to be ready.

*Did I say shorter at the beginning?

A day on Earth… 2.4 billion years ago

When the Earth formed, its atmosphere was very different from today. In fact, in the beginning it almost had no atmosphere at all. It took millions of years for the planet to cool down enough to start building up an atmosphere composed mainly by water vapour, carbon dioxide and nitrogen. Notice anything missing?

Exactly, no oxygen! The components of this early atmosphere came from the gases released from the molten rock. And one important detail: there was no life yet.

An early Earth may have looked like this. Peter Sawyer / Smithsonian Institution

The oxygen that is found in the atmosphere (O2) comes primarily from photosynthesis. The earliest evidence for life on Earth dates to about 1 billion years after the Earth formed. Early organisms were anaerobic, likely using methanogenesis or anoxygenic photosynthesis. Neither of these mechanisms release oxygen, but rather methane or sulphur components and water (Catling & Claire, 2005). The exact moment that oxygenic photosynthesis appeared is debated, especially considering that many fossils found are poorly preserved (Sessions et al., 2009). However, to get an idea, in fig. A there is a timescale showing the ages of fossils found, and possible moments when photosynthesis could have appeared, since cyanobacteria produce O2.

Fig. A: Timescale and ages of fossils. Sessions et al. (2009)

So what happened 2.4 billion years ago?

The oxygen levels in the atmosphere increased in what is known as the "Great Oxidation Event" (fig. B). The atmospheric oxygen went from 0.001% of present day levels to 5-18% by the time everything stabilised, some 1.8 billion years ago (Sessions et al., 2009). There was a second event that finally took the oxygen levels to present day levels about 500 million years ago.

Fig. B: A simplified view of the evolution of oxygen in the atmosphere. Sessions et al. (2009)

Now, cyanobacteria had already been doing photosynthesis and producing oxygen for some time (at least some 300 million years), but it wasn't building up in the atmosphere, at least not in the amounts shown by the geological records. This means that around this time there must have been a change: either there was an increase in the production of oxygen, or a change in the oxygen sinks to allow the O2 to remain in the atmosphere.  

One hypothesis relates the Great Oxidation Event with the changes in the tectonics of the planet that happened around the same time. Continental land masses stabilised towards the end of the Archaean (~2.5 billion years ago). Kump (2007) suggests that an increase in subaerial vulcanism is related with a reduced sink for oxygen, since before the emergence of continents most volcanic activity was submarine and more reducing (used up more oxygen). This is a compelling hypothesis because changes on the Earth of this scale (mayor continental change and substantial increase in atmospheric oxygen) happening at the same time are generally more than a simple coincidence. 

Why is this important?

Besides the fact that WE need oxygen to breathe, it is likely that complex multicellular life was able to evolve thanks to this: aerobic respiration is much more efficient than anaerobic fermentation (Sessions et al., 2009).

Catling & Claire (2005) also mention a couple of important things to consider:

• An early ozone layer in the stratosphere emerged once there was enough oxygen in the atmosphere (approximately 0.1% present day levels).
• Methane levels where high (simulations indicate 100 to 1000 times higher than present day), which kept the Earth warm, despite a "weaker" Sun. The rising atmospheric oxygen caused a reduction in methane, cooling the Earth down significantly, perhaps even causing  Snowball Earth conditions.  

This is only one of many mayor changes the Earth has gone through. In this case the intervention of newly appeared life played an important role in changing the atmosphere. However, as we will see in the next posts, one change can be followed by others that are unexpected.

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Other bibliography:

Tarbuck, E. and Lutgens, F. (1997). Earth science. Upper Saddle River, NJ: Prentice Hall.