Climate Change Questions - 2024 edition

[WYorksWeather]

Hi everyone, I know we've had one of these before, but inspired by some conversations elsewhere, I think it might be useful to start a new one, as the older thread is years old for the most part, and the last one went a bit off the rails.

However, I do think it's probably best that I propose a few guidelines for how we should have this work. I find that problems in most climate change discussions online tend to be with both the questions and the answers. You often get an aggressively-phrased question or answer, which then just leads to a barrage of rebuttals, counter-rebuttals, and then personal insults more often than not. It soon just descends into a pointless exercise.

In the interests of keeping a civil discussion, I'd like to tentatively suggest the following guidelines.

Guidelines for askers

• Phrase your question or questions neutrally
• Stick to one to three questions per post
• Indicate your current level of knowledge / how technical or detailed an answer you want
• If you make a factual statement, be prepared to support it

Guidelines for answerers

• Assume good faith
• Try to avoid overly long and/or technical posts unless absolutely necessary (I plead guilty to this!)
• Answer the question at the level of detail asked in the question
• If you make a factual statement, be prepared to support it

In addition to these, I'd also like to keep this strictly for questions and answers - general discussions about climate change should go elsewhere.

With the above in mind, fire away! Happy for anyone to jump in with questions or answers.

[LetItSnow!]

I love the idea of this and I hope that people can behave! I'll have to get my thinking cap on for some questions as I certainly am no scientist!

[Midlands Ice Age]

Thanks for this thread WYW..

 Can I ask my Arctic/ Antarctic  based questions in here and If so would I then be classed as a denier.?

I always try to use the data to lead me to conclusions, but that may not necessarily agree with certain people in here,  who think  GW is the key to every facet of the weather.

If you think I may be too contentious then I will happily stay away.

MIA

[WYorksWeather]

 Midlands Ice Age Absolutely no issue with asking questions in here - as long as they're in scope for the thread (in other words, more on how Arctic sea ice trends relate to climate change). A more detailed discussion of Arctic sea ice trends just in isolation (without a climate change angle) is probably better suited to your excellent thread on the topic.

I don't think you're too contentious - the point of this thread is to allow people to ask questions and have interesting discussions. It would be very boring if everyone who posts in here agrees.

The only limitation is just that I don't want to end up with the thread being derailed by people just shouting at each other and insulting each other, and from our previous discussions I can't see how that would be a problem.

[Methuselah]

How will a BAU scenario (as advertised very loudly by Trump & Co) cope with rising sea levels? I mean, the bulk of human civilisation is in low-lying areas. We can't all relocate to Denver, Colorado, can we? 

[WYorksWeather]

 Methuselah Interesting question. First, if we look at the Climate Action Tracker, we're looking for the sea level rise that corresponds to something like 3.0C above pre-industrial by 2100.

The sea level rise by 2100 under a scenario like RCP 4.5 which roughly corresponds to that, is about 0.7m. We've had about 0.1m of that so far. So that's another 0.6m (2 feet in old money). There is a lot more upside to that estimate than downside, as the relationship between temperature and sea level rise is much faster than linear. E.g. a 4C or 5C world by 2100 would mean several times as much sea level rise, not just a bit more. 

If we look at the Delta Works in the southwest Netherlands, we see how the Dutch are dealing with this. A common way of building infrastructure is to aim to withstand e.g. a 1 in 100 year event. Instead, this scheme has added a huge margin of safety. This quote from the Wikipedia article below explains:

Quote

The most important "dike ring area" is the South Holland coast region. It is home to four million people, most of whom live below normal sea level. The loss of human life in a catastrophic flood here can be very large because there is typically little warning time with North Sea storms. Comprehensive evacuation is not a realistic option for the Holland coastal region.

The commission initially set the acceptable risk for complete failure of every "dike ring" in the country at 1 in 125,000 years. But, it found that the cost of building to this level of protection could not be supported. It set "acceptable" risks by region as follows:

North and South Holland (excluding Wieringermeer): 1 per 10,000 years

Other areas at risk from sea flooding: 1 per 4,000 years

Transition areas between high land and low land: 1 per 2,000 years

River flooding causes less damage than salt water flooding, which causes long-term damage to agricultural lands. Areas at risk from river flooding were assigned a higher acceptable risk. River flooding also has a longer warning time, producing a lower estimated death toll per event.

South Holland at risk from river flooding: 1 per 1,250 years

Other areas at risk from river flooding: 1 per 250 years.

These acceptable risks were enshrined in the Delta Law (Dutch: Deltawet). This required the government to keep risks of catastrophic flooding within these limits and to upgrade defences should new insights into risks require this. The limits have also been incorporated into the new Water Law (Waterwet), effective from 22 December 2009.

You can see that they've built an absolutely enormous margin of safety into that. In short, they are (correctly) assuming that coastal flooding will become more and more common in the future, and so what seems ridiculous to build for now, is actually a precaution against the risk of future sea level rise.

And in fact, the Dutch are already going further (additional quote below):

Quote

In September 2008, the Delta Commission presided by politician Cees Veerman advised in a report that the Netherlands would need a massive new building program to strengthen the country's water defenses against the anticipated effects of global warming for the next 190 years. The plans included drawing up worst-case scenarios for evacuations and included more than €100 billion, or $144 billion, in new spending through the year 2100 for measures, such as broadening coastal dunes and strengthening sea and river dikes. The commission said the country must plan for a rise in the North Sea of 1.3 meters by 2100 and 4 meters by 2200.

In short, this only reinforces what a lot of people have already been saying - it's an enormously expensive undertaking to say that we should just adapt to climate change. So people who talk a lot about the cost of renewables, damage to the economy, etc., should also consider how much it would cost to adapt to very high warming levels and the associated sea level rise. And of course sea level rise is only one aspect.

[Midlands Ice Age]

WYW..

Regarding your suggested most important impact of CC being that of sea levels. 

How much of the sea level rise is due to the melting of Greenland (and afterwards presumably Antarctic)., as well as that adding  due to the continued  increased temperature of the oceans?. 

Also, I have always assumed that  the melting of the Arctic oceans sea ice will have little effect upon the sea  levels (due to S.G.), yet I have noticed one or 2 people mentioning the melting of the Arctic as being a factor in the other thread. 

Afterall it melts out almost totally in most years even now. Do we see annual change of sea ice affecting the sea levels during the course of the year today?

MIA

 

[John S2]

In answer to the question about causes of sea level rise, the main contributors appear to be:

1) Melting of land based ice 

2) Thermal expansion of the oceans

3) Reduction in water held on land - eg reduction in size of lakes and soil moisture

I have not been able to find a definitive answer on the percentages due to each of the above.

Melting of arctic sea ice should have no immediate effect on sea level, but presumably if the summer trend is downwards then increased heat absorption will be a positive warming feedback.

[Midlands Ice Age]

Thanks John 

I too have not seen anything documented.

But presumably someone must have modelled the various parameters. Otherwise how do we come up with any dates for this the most critical element of CC?

I guess I will have to look through the IPCC Climate change document!!.

I was hoping that one of the experts on here would have known the answer.

I do so much hope that it has not been 'parameterised'.

MIA

[WYorksWeather]

 Midlands Ice Age Sorry - missed your original question on Friday. I was out most of the day yesterday so only just had a closer look at the forum and seen it. Just to say as well that I think sea level rise is probably one of the bigger factors affecting the UK. Globally, in some of the hottest regions, probably temperature rises or aridity/desertification would be more of a concern in the decades ahead, e.g. southern Spain for example.

In answer to your question, this paper from 2018 is a decent source. 

First, the conclusions:

Quote

We present estimates of the altimetry-based global mean sea level (average rate of 3.1 ± 0.3 mm yr−1 and acceleration of 0.1 mm yr−2 over 1993–present), as well as of the different components of the sea-level budget. We further examine closure of the sea-level budget, comparing the observed global mean sea level with the sum of components. Ocean thermal expansion, glaciers, Greenland and Antarctica contribute 42 %, 21 %, 15 % and 8 % to the global mean sea level over the 1993–present period. 

So in short, it actually seems that mountain glaciers have had a bigger impact so far. This was a bit surprising, like you I thought it would probably be Greenland as the biggest contributor. But the more you think about it - the more it makes sense, because there is quite a strong trend for milder winters and hotter summers over many of the mountainous areas (thinking about Europe here, but the same will probably apply to North America and South America). And of course more anecdotally this can be seen in the various 100-year comparison photos of various mountain glaciers across Europe and North America. The paper does mention in the main section though that glaciers will decrease in importance through the 21st century compared to other factors.

The various forms of ice loss are slightly greater than ocean thermal expansion, but as the paper notes, there is still some uncertainty about the remainder (you will no doubt have noticed that 42% + 21% + 15% + 8% = 86%), so there remains some to be explained via uncertainty or other smaller factors.

I would note that Arctic sea ice doesn't get much of a mention here - I've seen before that it could have a very small impact due to differences in density between freshwater and seawater. This NASA article puts it at something extremely small like 1mm in total, so it's really not something to be concerned about on a broader scale (though no doubt interesting for scientists in trying to close out some of the small remaining uncertainties).

In terms of sea level rise, it's the acceleration component that is more significant in terms of future trends. There is some uncertainty in this, but if you do a trivial extrapolation starting with average sea level rise of 3.1mm per year centred on 2005, then by the end of the century, with an acceleration of just 0.1mm per year, sea level rise would be about 12mm per year (about half an inch per year in old money). By a fairly simple bit of maths to produce a trivial estimate, you would then get further sea level rise above 2005 levels averaging 7.5mm per year over the 21st century, which extrapolates to a couple of feet of sea level rise.

The key uncertainty in future trends is the stability of Greenland and the Antarctic under the very high warming scenarios, hence this graph from the IPCC. It will be a case of more observations needed, but I think there's enough evidence here to say that at the very minimum, any new long-term infrastructure which we expect to still be around in 2100 should probably be built with a couple of feet of sea level rise in mind plus a significant buffer above that.

As an example of the sort of decision-making that might be needed with a high-profile project - the Thames Barrier is expected to need upgrading or replacing before the end of the century, with a decision on what to do planned for 2040, to allow plenty of time for construction before the Thames Barrier is expected to be less able to protect London, by around 2070.

Of course such investments are not cheap - the government recently spent £80m on the Dawlish sea wall to protect that vulnerable railway route, for example. This reinforces my point that whilst adaptation is possible, it's certainly not a cost free option.

Let me know if you have any further questions, or indeed if I've not quite answered the intended question!

 

[Midlands Ice Age]

Could you send a link for the above paper please?

MIA

[ANYWEATHER]

Didn't the last major sea rise occur 10.000 years ago after the last ice age  and the last 7.000 years sea level rise has been pretty stable .....? ☺

[Methuselah]

 ANYWEATHER But it isn't stable now -- it's rising.

[WYorksWeather]

 Midlands Ice Age Good spot - after all that, I forgot the link 

Here you go: https://essd.copernicus.org/articles/10/1551/2018/essd-10-1551-2018.pdf

[WYorksWeather]

 ANYWEATHER Sea level rose by about 120 metres from 20,000 years ago to around 10,000 years ago (some sources say 8,000 years ago), which is a rate of about 12mm per year. The current rate of increase is around 3mm per year, and is steadily accelerating as the paper above mentions, by around 0.1mm/y^2.