The Ocean Engine: Climate Change

Showing posts with label Climate Change. Show all posts

Tuesday, 10 January 2012

The Ocean Engine: The Finale

It is now time to wrap up and conclude this blog. As stated, the aim of this blog was to explore past changes in ocean circulation; past, present and future. At the beginning of this blog, we sought to define the ocean’s role in the climate system. In particular, I stressed through the concept of the conveyor belt that whilst analogies are good for framing our imagination of ocean circulation, it is important to reconcile that the ocean is a complex mechanical engine in reality. Furthermore, this blog also reviewed techniques in palaeooceanography, to understand how past changes in ocean circulations are reconstructed. Upon reflection, given more time, I feel I could have perhaps added a few more detailed post attached to this topic as it is of crucial importance to understand past changes in ocean circulation.

This blog then explored paleaoclimatological evidence for past changes in ocean circulation. In particular, several episodic were analysed in relation to abrupt climate change; The Younger Dryas, 8.2 ka event and the Late Cretaceous. In this respect, I did narrow my research stand of the “ocean circulation” with respect to the North Atlantic circulation. However, this strand of blog posts could be nicely conceptualised by the posts I did on millennial-scale climate change. I found this strand of research particularly fascinating, given the complexity of feedback processes revealed from ice core studies such as the bipolar seesaw mechanism.

In this respect though, I feel I potentially could have explored two more strands of research in The Ocean Engine; notably the Southern Ocean and the El-Nino southern oscillation, both key are important components of the ocean system in relation to the past and present components. However, I feel that my definition of The Ocean Engine evolved over the course of this blog to run along the following theme; despite popular views advocated in films or by climate skeptics, ocean circulation is a complex science in reality. Thus through focusing on the North Atlantic thermohaline circulation, this blog sought to disentangle the myths attached to this component of the climate system by adopting a palaeo-approach and trying to understanding potential future impacts associated with anthropogenic climate change.

One of the key take-home messages from this blog is that by adopting a palaeo perspective, this can provide a critical position to interrogate questions surrounding climate change. The study of paleoclimatology differs somewhat in ideology to that of modelling, as emphasised in various posts. This divergence is a crucial point to convey a very key message; that anthropogenic climate change puts our understanding of the earth’s climate system to the limit, and we are currently at a stage to make fairly accurate predictions at the impacts but a significant distance away from the goal of quantification. I exemplified this point nicely in the last post, through the concept of noise, which I feel is useful analogy to help explain why uncertainty exists in climate change science; a crucial ingredient to any debate on climate change.

It has been an absolute pleasure writing this blog, and it has enriched my understanding of ocean circulation in relation to debates on climate change. To conclude, whilst we only are beginning to understand the components of The Ocean Engine, we do not understand its interior mechanics and complexities as of yet. Arguably, there are surprises in store as our understanding of the system develops and this warrants the seed for further research!

Monday, 9 January 2012

Conceptualising the ocean’s role in the climate system

Whilst we have been attempting to understand changes in ocean circulation due to climate change, it is useful to present a brief sketch of the earth’s climate system. The earth’s climate demonstrates variation on a variety of timescales, scaling from interannual, interdecadal, interannual, millennial and geological scales (Mann, 2007). Thus, the variation of the Earth’s climate can be conceptualised as the product of exogenous (factors independent of anthropogenic change and/or changes in other variables) and endogenous variables (factors affected by anthropogenic change and/or changes in other variables).

In relation to this conceptualisation, ocean circulation can be understood as an endogenous factor in the earth’s climate system. Given that the current timescale of the Holocene (for purposes of simplicity this term is invoked) is shorter than that of orbital variations (eccentricity, precession and obliquity), termed “Milankovitch pacemakers”, events which occur at “sub-milankovitch periodicity” must be invoked to account for Holocene climate variability. Solar radiation and volcanic eruptions can be understood as examples of exogenous forcing factors and greenhouse gas emissions, EL Nino and Southern Oscillation (ENSO) are examples of endogenous forcing factors.

An interesting point in the debate is that of attribution; Is climate-change natural and /or anthropogenic driven? Crowley (2000) running a model similar to that of the IPCC, found that over the last 1000 years, solar forcing and volcanic forcing explained 41 – 59 % variance. However, when including greenhouse gas emissions and tropospheric aerosols in that scenario, it explained 41-64% of variance.

A question you may ask then is what accounts for the remaining 36 %?

I would argue that most of the uncertainty in the climate change debate is that it is difficult to attribute any degree of climate change conclusively to internal or external factors due to “noise” in the climate system. This can be defined by the fact that multiple possibilities exists for conceptualising the response of the climate system to a specific exogenous or endogenous forcing factors (Maslin and Christensen, 2007) (Figure 1). The climate system may respond directly in response to a variable (Figure 1a), in a delayed fashion (Figure 1b), a muted fashion (Figure 1c) or after passing a threshold (Figure 1d). To complicate this further, bifurcations exist, whereby forcing required to go through a threshold is different to the reverse, implying that once a threshold has crossed, it is difficult to reverse. This can be inferred from previous posts in relation to the impact of meltwater on the deep-water circulation.

Figure 1: Four Possible responses of the global climate system to forcing factors a) Linear b) Muted C) Non-Linear and D) Threshold.

Source: Maslin and Christensen (2007).

Whilst each element of the climate system may respond in variety of ways described above, this is compounded by the fact that each factor in the climate system responds on a different timescale. In this sense, the climate system is anti-essentialist in a way, the nature of climate system respond is multiple and complex.

This conceptualisation illustrates the complexity of climate change science in particular in response to the question of attribution; detangling the greenhouse signal from that of natural climate variability.

Surpises part 3: A Collapse of the thermohaline circulation?

Given the potential of the north atlantic thermohaline circulation (NATHC) to influence climate change as evident from study of abrupt climate changes from paleo-records, the following question is thus posed; will the NATHC collapse due to a rise in greenhouse gas emissions? The concern over the impact can be understood by the logic that an increase in sea surface temperatures due to thermal expansion of the oceans, may in turn reduce the solubility of CO₂ in warmer waters (Stocker et al. (2000 in Seidov et al., 2000). This in turn, may create a positive feedback effect whereby warmer waters hold less inorganic carbon, thereby causing a CO₂ release into the atmosphere (Stocker et al. (2000 in Seidov et al., 2000).

One issue in trying to understand this prediction through modelling is that it is difficult to achieve such a timescale. However, one of the earlier studies; undertaken by Manabe and Stoffer (1994), use a comprehensive atmospheric-ocean general circulation model (AOGCM) to simulate the impact over many centuries. Their results appear to indicate that a critical threshold lies between a doubling and four-fold increase in CO₂ concentrations. However only models of reduced complexity can be used to aid quantification of threshold, as this may allow for long-term simulations.

It has found that in addition to the stabilization level of greenhouse gas concentration in atmosphere, rate of greenhouse gas emission increase may also help determine a threshold. This is illustrated in Figure 1 with a simulation run by Stocker et al. (2000 in Seidov et al., 2000). They set climate sensitivity at 3.7 ° C for doubling of CO₂, and simulations of run concerning the rate of CO₂ increase a in 1 %/yr, 2 % year and 0.5 %/yr scenario (Figure 1a)

Figure 1a) Atmospheric CO₂ simulations for five experiments b) Simulated global mean temperature c) Simulations of maximum meridional overturning of the North Atlantic in Sverdrup (1 Sv= 10⁶ m³/s).

Source: by Stocker et al. (2000 in Seidov et al., 2000)

The global mean surface air temperature in simulations is not dependent on emission history for maximum CO₂ concentration (Figure 1b). However, a bifurcation appears apparent concerning the maximum meridional overturning of the North Atlantic. Reduction is apparent in all scenarios with the level dependent on maximum CO₂ concentration and CO₂ increase according to scenario. The circulation collapses at 750 ppmv with increase at rate of 1%./ yr. It then subsequently, appears to recover and settle to reduce value if increase is slower (0.5 %/yr ) or if the CO₂ level is reduced to 650 ppmv. At a rate of 2 %/yr, the circulation appears to collapse. The simulations appear to indicate that once the THC collapses it may settle a new equilibrium, with irreversible changes occurring, independent of CO₂ concentrations.

However, it must be noted that there is huge degree of complexity in understanding the impact of future changes in the thermohaline circulation due to anthropogenic climate change. These include; a lack of understanding concerning the variety of feedback mechanisms associated with changes in the THC and palaeoclimate modelling. There is a need to quantify components of climate-related components to a signal and test hypotheses regarding science of abrupt climate change. Changes in THC are likely in future and it is known the slowing down of THC moves system closer to thresholds. The uncertainty and importance attached to this as detailed in past blog posts highlight the need for further research.

Sunday, 11 December 2011

What does Durban mean for the world?

So the news is out. After a frantic extra day of negotiations that continued late into Saturday night, a deal has been struck. So what exactly is this all about?

In a nutshell:

The EU came to Durban calling for a mandate to negotiate a legally binding deal on climate change by 2015.
However, EU clashed with India and China over the legality of a new agreement, threatening to put the talks between 194 countries into jeopardy.
The EU wanted to push a “roadmap”, which would establish a new over-arching agreement that would commit countries to emission cuts. India and China, expressed concerns at the legality of such proposals, preferring to adopt the term ‘legal outcome’ as oppose to “legal instrument” in the agreement (The Guardian, 2011).
After the South African President urged the EU and India to go into a huddle to resolve the language dispute, a Brazilian compromise saw an agreement between both parties to negotiate another legal instrument or an ‘agreed outcome with legal force’ (The Guardian, 2011).
The treaty will be negotiated by 2015 and implemented from 2020. It will also allow action to address the emission deficit between voluntary reductions and those experts state are needed to tackle climate change.
As a side issue, ministers had agreed that by 2020, a $ 100 bn fund to help countries move to a green economy and tackle the effects of climate change in addition to measures to protect forests and develop global markets.

These talks are part of a series of wider issues; and I have neatly summarised them below. The figures are referenced by Mark Maslin’s ‘Global Warming: A Very Short Introduction’, a very accessible text exploring all dimensions of the issue.

Why do we need a legally binding agreement?

- Legally-binding multilateral agreements through the United Nations Framework Convention on Climate Change to cover emissions from all countries are the only viable way to keep an increase in global average temperatures since pre-industrial period below 2 °C, a threshold widely agreed to mitigate "dangerous" climate change.

Why the urgency for a legally binding agreement?

To summarise climate science, the earth has a thermal lag meaning so even if emissions stopped today; the earth’s temperature will still rise (Current estimates are we have experienced 0.5- 1°C warming already).
The political issue is essentially a game of risk; what temperature and hence, CO₂ concentration do we aim for?
A ‘two-degree’ world is seen as the threshold as scenarios based on temperature rises beyond this to 3, 4 , 5 and 6 °C will involve a complex series of feedbacks that will affect humanity’s ability to adapt to climate change.
In order to reach 2°C, we need to peak global emissions by 2015 at a CO₂ concentration of 400 ppm (we are currently at 390.91 ppm). Thus, a legally binding treaty is required to give any hope of achieving this (or staying in the 2-3 °C margin).

Why the difficulty?

As witnessed at the Durban talks with the conflict over the use of language between the EU, China and India, there are some key issues in such global negotiations I would like to point out:

Trust: The developing countries and ‘fast-emitters’ (e.g. India and China) are concerned by ‘green colonialism’, the concept that developed countries should dictate to developing countries how they should develop and what action they should take, actions they feel will supress their right to a fair development trajectory.

Geopolitics: As China rose at the talks, they felt the EU’s roadmap proposals would be mostly beneficial to the US. Multilateral talks need a global political view. The US’s importance, economically, politically and as a large emitter, requires its participation in order for a global community to develop on climate change.

Leadership: Tied in with the above, a united long-term vision is required from political leaders across the globe. That even in an era of economic austerity, a long-term vision and pathway must be clearly set to adapt to climate change to prevent a future social, economic (potentially greater than the recession), environmental and political catastrophe.

What should an agreement include?

To briefly conclude. The Durban summit could be looked back on as a success if the negotiations on a treaty outlined in the talks are implemented. So what could this include?

- Contraction and Convergence

This is the idea proposed by Meyer (2000) that the largest emitters of greenhouse gases contract the level of pollution towards an agreed per capita emissions total. For example, the US CO₂ emissions/person are 10 times that of China. As a global community, we need to try and keep the amount emitted per person the same. Therefore, every country has to contract their emissions, some more than others. For the developed world, this means a low-carbon economy is a serious alternative. This agreement should be open and transparent and include the developing world in order to invoke the concept.

- A Green Economy

Carbon markets, initiated in Kyoto, need to become global carbon markets in order to accelerate capital flows from the developed to developing world. I believe the concept of a green economy can act as a framework by developing global institutions that allow the development of such markets, renewable energy technologies and capital flows between the developed and developing world. This would accelerate the capitalist system to accelerate a positive response by encourage investors and other actors in the private sector, and minimise the regulatory risk that has been witnessed for more than a decade as the world just watches conference after conference of inaction.

Chris Huhne, the UK climate change secretary, said the deal represented a “significant step forward” (The Guardian, 2011) . Let us hope he is right….

The Ocean Engine