Your web browser (Internet Explorer) is out of date. Some things will not look right and things might not work properly. Please download an up-to-date and free browser from here.

Dr James Renwick responds to your Climate Change questions

Dr James Renwick of NIWA responds to your questions relating to Climate Change. thanks Dr Renwick for taking the time to answer the many questions sent in by our readers.

Dr Renwick’s replies are in italics.

From Dave:

1. I recently read an article about the fact that the sun appears to be going into a period of hibernation, that is the activity levels are dropping. The article suggested that this will result in a period of significant cooling on earth. Doesn’t it seem strange that the sun is responsible for cooling but not warming?

JR:  The sun is responsible for cooling and warming, depending on whether it is dimming or brightening.

Maybe the proponents of global warming don’t want to recognise that as it doesn’t suit their purpose?

JR:  Not at all, it is a key component of the global energy balance, and solar variability must be factored in to all calculations. Certainly all the model runs take careful account of this. But, solar output hasn’t varied much lately (beyond a small decrease), so hasn’t had much of an effect. Yes, the sun has been quieter the last few years, and yet the last decade was the warmest on record. So, something else must be going on – greenhouse gas increase.

From KaVe:

1. Is their any influence from the sun?

JR:  The sun drives all climate, and all life on earth. Solar output is relatively steady from year to year, but varies on various longer time scales (the sunspot cycle etc). Lower solar output (sunspot minimum) goes with a reduction in temperature and higher output goes with a higher temperature, other things being equal.
2. How do scientists actually “read” e.g. ice- and seafloor-cores to make statements about the Earth’s past climate changes?

JR: Through various ingenious methods. These often involve chemical analysis, such as studying ratios of different isotopes of chemicals (e.g. oxygen-18 vs oxygen-16) because the ratio can depend on temperature.
3. How the current climate change is different from the past ones and why this one is (or is not) so dangerous for us?
JR: Mostly it is different from the past because it is very rapid. It’s an issue for us because we’re here this time!  Civilisation has grown up in the last 10,000 years, when the global climate has been quite stable. The last time there was a lot of global climate change, during the peak of the last ice age cycle, the human population was numbered in the millions at most. Now, we’re looking at significant climate change (including changes to where crops will grow, where rain falls etc) with 7+ billion people. As a species, we have come to depend on the climate being like it has been the last few centuries. A lot of change will mean a lot of disruption to agriculture, water supplies etc.
4. What is the difference between ‘climate change’ and ‘global warming’?
JR: Climate change is a broader term. Global warming refers only to temperature, while climate change covers all elements – rainfall, ice, snow, oceans, etc.
5. Explain why ‘climate change’ is not something that you ‘believe in’ but you except as a fact, based on robust, peer reviewed scientific data, or do not except based on other robust, peer reviewed scientific data.
JR: Because it’s a scientific study/idea. All of science is built on observations, and deductions, hypotheses, not on faith or belief.

From Allan:

1. How can a tax payment on climate change stop global warming?

JR: Climate change is happening because of greenhouse gas emissions. To stop it or reduce it, we need to reduce the greenhouse gas emissions. And we have to start somewhere. A carbon tax pushes economies in the direction of reducing emissions.

From Anon:

1. It seems to me that there are more earthquakes, more frequently or being reported of more? Can you please give me more insight into this as, Melbourne just had one today, they’re happening what feels like all over NZ. Surely more natural disasters are impacting because of climate change perhaps.

JR: There are no well-known links between climate change and the solid earth (earthquakes, volcanoes etc). Some have speculated that melting ice and adding to sea level changes the distribution of mass on the earth, so that can change the forces on tectonic plates and possibly have an effect on earthquakes. But there’s no strong evidence of that as yet.

From Phastbaque:

1. Is the recent volcanic activity expected to have a climatic change or even a weather impact?

JR: Unlikely, as it hasn’t resulted in significant blocking out of sunlight over a large area of the globe.
2. Do we know what the climate changes are going to be and what sort of time frame?
JR: Yes, in broad terms. The IPCC reports cover this in some depth. Look at and have a look at the 4th assessment report, Working Group 1. The latter chapters cover global and regional changes in detail. Also, the local MfE web site has a lot of stuff on this for NZ.
3. Do we need to look at moving food sources to different locations?
JR: Yes. This will no doubt happen as growing conditions change.

From Larry:

1. In geology terms, weather patterns have existed for countless millions of years however in technical terms, reliable weather gauges and meters have existed for less than one hundred years. With such a huge gap, how can scientists promote the certainty of climate change without conclusive data?

JR: We can study the past using proxies, like tree rings, ice cores etc, and build up quite a coherent picture of the climate back over hundreds of thousands, or even millions of years.

2. While people choose to live on flood plains, reclaimed swamps, past hillside slips, eroding coastlines, sand starved islands, etc, we will hear about extreme weather, climate change or even global warming. This century would be a speck on a geology time line so how do scientists determine that we are entering another ice age when we could be just leaving it?

JR: We left the last ice age about 18,000 years ago – this is well known from ice core records. The last 10,000 years (the “Holocene”) has been a period of stable global climate, allowing the development of modern civilisation. We would be due to go in to another ice age in the next few thousand years, but the extra greenhouse gas in the atmosphere now is estimated to have postponed that ice age by at least 20,000 years or more.

From Anon:

1. Does the activity of the sun influence our temperature on earth and if so can the cooling down of the sun or a quiet period help us with Global Warming?

JR: Yes, a quieter sun could help reduce temperature rises. But, the sun has been relative quiet the last few years and the past decade has still been the warmest on record.

From ChrisMB:

1. I’ve been reading lately that many of the planets in the solar system are heating up. Do those that believe we are contributing to climate change, think that maybe they were off the mark – given that other planets and moons are also warming up?

This article dates back to 2007 ( yet we’ve been trumped as “the main cause” of this. It has propelled so many taxes, revolutions and guilt-tripping over the past 5 years or so.

Benny Pieser from John Moores University was quoted as saying “Perhaps it is a fluke”. That to me is a cop-out – multiple planets/moons experiencing the same thing at the same time. For those that are so certain that the science stands behind them on it, the fluke comment really isn’t a scientific response.

I’m interested in Dr Renwick’s answer in what correlation there is/is not between earth’s warming and other planets and moons in our solar system.

JR: I don’t think there’s a correlation. The physics behind greenhouse gases and climate change on earth is pretty fundamental. It’s easy to think “many of the planets are heating up”. It turns out maybe a few might be, and maybe others are cooling. We don’t have much detailed information on the other planets. Either way, the sun has been slightly decreasing in output lately, so warming is unlikely to be due to solar changes. See for more on this.

Fact: NASA discovered planets are heating up.
Fact: Earth is heating up
Claim: Humans are largely responsible for earth heating up.
Question: If other planets are heating up, why are we responsible for earth?

JR:  See above.

From Mervyn Merrilees

1. Global temperature records based on land and sea measurements do not appear to be particularly reliable, and are often at variance with regional measurements. In both cases, however, adjustments have been made that are not easy for others to understand and have lead to arguments as to veracity. For global measures, the inclusion of proxy measures, such as tree ring data, has been challenged. Satellite measurements appear to be more reliable, but are short term and began at a low point in the recent temperature record, so don’t yet provide predictive power. Data from the USA show that the 1930s was likely as warm, or warmer, than this recent period of warming.

Given the questioning of global and regional temperature records, in your opinion, what is the best data set that unequivocally shows that the current warming (since the 1980s) is exceptional and outside the limits of natural variability experienced over the past 100 years, or indeed 1000 years?

JR:  It’s important to distinguish between regional and global change. Regional temperatures can change, and cancel each other out (cold in Melbourne, warm in Auckland, for instance). This happens because heat can be moved around by the oceans and the atmosphere, with no net change in the total amount of heat. But when we see the global average rising, that can’t be due to heat being moved around within the climate, it must be due to a change in the overall amount of heat energy available. So, global averages are the most important indicators of global climate change. Over the past century, the instrumental record is the best, but beyond that, tree rings, lake sediments, ice cores etc provide good proxy indicators going back many centuries.

2. During the 80s and 90s, and early this century, various climate models predicted that global temperatures would increase significantly due to rising CO2. Over the past decade, however, (since 1998) it is generally acknowledged there has been increasing divergence of temperature records from model predictions, with no increase in global temperature, and possibly a decrease.

Given the lack of warming over the past decade, at what point do you think the climate models should be reassessed and the relationship between CO2 and temperature questioned?

JR:  “The lack of warming over the past decade?” The last decade is the warmest on record globally, followed by the previous one, and the one before that. Sea level rise continues without a pause. There is very little sign that global warming has ceased.

3. Predictions of catastrophic events resulting from warmer temperatures include rapidly rising sea levels, increased number and severity of cyclones/hurricanes, and increased extremes of both flooding and drought. Yet throughout this current warming period (ie past 30 years) the data indicate little change in the rate or frequency of these predicted events or indeed, movements opposite to predicted direction. For example the rate of sea level rise, according to Colorado data, is in fact slowing (despite their recent adjustment for land rise). Similarly for cyclone data, there does not appear to be any detectable increase in cyclone severity or total cyclone energya, although possibility an increase in number due to better detection of smaller cyclones. Measures of cyclone energy actually appear to be inversely related to warming. It was also predicted that snow cover would decrease (and for children in the UK, it was claimed a few years ago that snow would be a thing of the past). Yet snow extent in the northern hemisphere has not decreased; since 1967 it has marginally increased.

How much credence do you give to predictions of catastrophic changes – that is changes outside of the extremes already experienced over the past century?

JR:  Globally, sea level rise has not slowed – just the opposite. See for a very nice summary. The number of very intense cyclones appears to be increasing, and the frequency of heavy rainfalls has been measured to be increasing in many parts of the world. As the globe warms, there’s more energy available to weather systems, so the chances of intense storms and heavy rains etc increases. So what may have been the 1-in-100-year rainfall becomes the 1-in-50-year, or 1-in-25-year rainfall by later this century.

In your opinion, do you think data from reactive global surrogates for temperature, such as rate of sea level rise and extent of snow cover, are more useful measures than the temperature record?

JR:  In some way yes, as they smooth out a lot of the fluctuations in temperature that come from episodic events like El Nino. So, the longer-term trend is more obvious.

4. CO2 has been identified by climate scientists who believe the current warming is exceptional as the primary driver of temperature, with changes in sun activity contributing only a small amount. Yet recent data show increasing divergence-of-fit between CO2 levels and temperature, but a strong correlation with sun cycle activity. Very recent publications provide very good data showing a marked decrease in sun activity and the authors predict that this could impact negatively on global temperatures and be clearly noticeable in about a decade, at the beginning of sun cycle 25 – which may not eventuate – and possibly extend for several decades.

JR: See above – the sun’s output has decreased lately while temperatures continue to rise.

In your opinion would you rate CO2 as the primary driver of temperature, or do you think sun activity has a greater impact?
JR: Right now, it’s CO2. But at other times in the past, the sun has been the key player.

Do you think predictions of a marked cooling in the relatively near future, based on observations of patterns of sun activity, have any foundation?

JR: No. The effects of all the extra CO2 in the atmosphere would easily outweigh the relatively small changes in solar output that have been observed or are expected.

5. NZ’s EST and the Australian proposed carbon tax are based on the premise that CO2 is the driver of climate change and reductions in man-made CO2 emissions will stop and hopefully reduce temperature increase. My rudimentary calculations show that this is impossible as any change in temperature would not be measurable with current instruments, and would be meaningless when measured against a background of natural variability.

JR: What are the calculations based on? CO2 concentrations (and those of other greenhouse gases) are fundamental to the climate. Take away the 0.039% of the atmosphere that is CO2 and surface temperatures would fall away sharply. Raise the concentrations significantly (as we are doing) and significant temperature rises will ensue.

Has NIWA calculated the net effect of our ETS on predicted global temperatures, and has NIWA calculated the effect on global temperature if our scheme was world wide?

JR: No – the point of an ETS is to get economies moving in the direction of reducing emissions. It’s very much a first step on a long road. But we must start somewhere.

Why are only selective weather events ‘consistent’ with global warming but not others? Is this because those events that are supposedly ‘consistent’ actually lack data to show otherwise?

JR: Not that I’m aware.

I remember statements made some years ago that warming was almost certainly the driver of Katrina and that we would see many more such storms. As we now know that was not true. So, seems to me that the only way of properly handling uncertainty is not not speculate but to collect data.

JR: Indeed.

The second point concerns the statement that the Greenland ice sheet lost more mass last year than any year in the last decade. So question is:  If the Greenland ice sheet is losing mass faster than at any time over the past 10 years, where is the water going to?

JR: Into the oceans. Sea level rise is now more than 50% due to ice melt, according to the latest information I’ve seen.

The predictions have been loud and clear that the loss will increase sea level. Yet the data show otherwise. The rate of sea level rise is decreasing – according to 5 recording systems. So something doesn’t fit?

JR: Which recording systems? Global sea level rise shows no sign of slowing. See

Again, our big thanks to Dr Renwick for taking the time to answer the many questions.  Feel free to discuss in the comments section below.  Comments that involve nasty personal attacks will not be published.



ChrisMB on 18/07/2011 11:44pm

Thank you Weatherwatch and Dr Renwick…

One thing to note: The links supplied end up at a webmail login for (The Radio Network) 🙂 I’ve managed to get to the articles…but I’m a geek so I know how to strip out the mail portion.

I appreciate Dr Renwick’s responses, however I still remain unconvinced.

I see the answers re: the sun’s output is decreasing, if anything.
One question this brought to my mind is, what about the sun’s size? I’ve seen articles that the sun is increasing in size – so if the output is dropping but the size is increasing, would this not still have a heating effect on the earth?

The whole subject is fascinating from a skeptic point of view 🙂

WW Forecast Team on 18/07/2011 11:52pm

Thanks Chris – the links are all fixed now, apologies for that.

Dr Renwick is overseas for the next few weeks but we’ll definitely raise your question with him next time we speak.  Great that you’re enjoying the debate!

– WeatherWatch Weekends

ChrisMB on 19/07/2011 12:07am

That would be super 🙂

Is there a way to get email notifications when new replies are made to posts or do I need to keep tracking this one?

WW Forecast Team on 19/07/2011 12:19am

You’ll need to keep tracking this one Chris – but if we get James to respond we’ll put this back on the homepage.  In fact it will likely be placed back on the homepage this week but then may not appear for a few weeks until James is back.


Philip Duncan

sw on 16/07/2011 6:13am

At least both “believers” and “unbelievers” of this topic get their views aired on this site and hopefully a healthy debate.Good to see a Q&A both sides.

David on 16/07/2011 3:40am

I agree, a very well done question and answer session, well done James I take my hat off to you and those who asked the questions.
It would be very good to have a perception of balance by having a person to answer questions who is from the point of view that warming or climate change is NOT from the influences of the Human race.
I would be sure that they would not come from the so called “factless propaganda brigade as suggested by RW.
Maybe we could have one of the thousands of scientists who are of the alternative views that have been silenced and are not from government funded organisations such as NIWA.
I disagree that we often hear of cold snaps in South America on the news, in fact if you look at the history of both TVNZ or worse still the BBC, we more often than not hear of the hot spots, very unbalanced in my view anyway, of course the BBC is government funded so they must follow the political agenda given them.

So WW, what do you say?
To show a balance it would be great to have the alternative point of view questioned.

Again well done James and thankyou.

WW Forecast Team on 16/07/2011 3:45am

Hi David – yes we are looking in to this now to ensure we remain fair and balanced.  We have another story tomorrow with a counter discussion on Climate Change.

– WW

RW on 16/07/2011 2:41am

Congratulations to Jim Renwick for a simply and elegantly put series of answers. If these persuade even one person to abandon their attachment to the fact-free propaganda so freely put about by the “sceptic” industry, the exercise will have been worthwhile.

For those who never look at these reports, the NOAA one for June is out:

Note for example how the red temp. anomalies in South America outweigh the blue ones – the media are very fond of publishing “cold snap” stories from there, with never a mention of other parts that are roasting in above-normal temperatures. June 2011 was the 316th (or thereabouts) consecutive month with global means above the 20th century mean.

westcoast on 16/07/2011 8:44am

As Jim said, you get places with hotter than normal, and on the other side of the weather system that caused that you can get a place that is colder than normal
the Net effect will be no change (they cancel each other out).Thats on a regional scale. But if the net effect globaly is increasing temperature, then that points to warning occuring to increase in green house gases (as he says, given all else being equal (e.g solar output)

Related Articles