Are humans heating up the world?

I was in Australia over Christmas-New Year period and the southern parts of the country were sweltering in a heat wave. Yesterday, the Australian Bureau of Meteorology issued its 2018 climate statement, revealing a record breaking run of rising temperatures. The graph below shows average Australian temperature by year relative to the 1961-1990 average temperature.

The average maximum temperature for the country as a whole was particularly warm, 1.55 degrees Celsius above the 1961–1990 average, making 2018 Australia’s second warmest year on record for daily high temperatures. Nine of the ten warmest years on record have occurred since 2005. These rising temperatures have been accompanied by drought, bushfires, and the death of half of the Great Barrier Reef.

I was astounded to read the comments to an article in the Sydney Morning Herald on this, where many commentators expressed complete disbelief that the climate was changing, or that humans were responsible, or indeed that the science was settled and not in dispute. A recent major report by the Intergovernmental Panel on Climate Change  stated that human activities are estimated to have caused approximately 1.0°C of global warming above pre-industrial levels, with a likely range of 0.8°C to 1.2°C. Global warming is likely to reach 1.5°C between 2030 and 2052 if it continues to increase at the current rate. Achieving the global greenhouse gas emission targets set in the Paris Agreement will limit global warming to below 2°C this century.

The report also makes clear that limiting warming to 1.5°C will have huge benefits compared with allowing temperatures to surge to the 2°C level. But keeping to 1.5°C would require aggressive action to curb greenhouse gas emission, going further than the targets set in the Paris Agreement. Even if nations could achieve that, the world would look very different: entire ecosystems could be destroyed across more than 6% of the earth’s land surface, sea levels would rise between half and 1 metre, and 70–90% of coral reefs would disappear. Moreover, sea levels will continue to rise for centuries, with projected long term increases in the range 3-13 metres.

The  most important greenhouse gas is carbon dioxide, and the Keeling Curve summarizes the global accumulation of carbon dioxide in the earth’s atmosphere. It is based on continuous measurements taken at the Mauna Loa Observatory on the island of Hawaii from 1958 to the present day. The curve is named for the scientist Charles David Keeling, who started the monitoring program and supervised it until his death in 2005.

Source: Delorme [CC BY-SA 4.0 (, from Wikimedia Commons

This is one of the most important scientific results of the 20th century. It was the first significant evidence that carbon dioxide levels in the atmosphere were rapidly increasing, and in a very real sense it continues to track our performance as a species. The curve continues to rise steadily at an undiminished pace, and is a stark indictment of a species that is ready to stand by as islands submerge, coastal lands flood, human habitats burn in wildfires, entire ecosystems disappear, species extinction accelerates, and coral reefs disappear.

Data from Antarctic ice cores has enabled levels of carbon dioxide to be measured back to 800,000 years ago. The graph below shows 800,000 years of CO2 data, based air bubbles trapped in ice cores. It shows that CO2 hasn’t ever been greater than 300 parts per million, with very slow and cyclical increases and decreases about every 100,000 years. Today it’s over 400 ppm, 33% higher than it’s been in 800,000 years, and on a very sharp upwards trajectory.

                                                                                                                                                                Credit: Scripps Institution of Oceanography.

A 2009 study, published in the journal Science, analyzed shells in deep sea sediments to estimate past CO2 levels, and found that CO2 levels have not been as high as they are now for at least the past 10 to 15 million years, during the Miocene epoch.This was a time when global temperatures were substantially warmer than today, and there was very little ice around anywhere on the planet. And so the sea level was considerably higher — around 100 feet higher — than it is today.

With global CO2 emissions continuing on an upward trajectory that is likely to put CO2 concentrations above 450 ppm or higher, it is extremely unlikely that the steadily rising shape of the Keeling Curve is going to change anytime soon. Particularly, as the United States has repudiated the Paris Agreement and started dismantling climate change regulations. Australia also recently abandoned emissions targets or any policy to address climate change, effectively also abandoning the Paris Agreement

National emissions have risen each year since 2014, when the Australian government repealed laws requiring big industrial emitters to pay for their emissions. There are also no significant policies to reduce the other major sources of pollution, such as transport, agriculture, heavy industry and mining, which together generate nearly two-thirds of Australia’s carbon emissions. Australia’s conservative government has rejected four national climate policies since it was elected in 2013, and rejection of climate change policy arguably played a role in the abrupt replacement of then Prime Minister Malcolm Turnbull by a climate sceptic Scott Morrison.

The Australian government refusal to act on emissions is completely out of line with public opinion, with a recent poll finding that 68% of respondents wanted domestic climate targets in line with the Paris Agreement. Australia is among several industrialized nations that are not on track to reduce greenhouse gas emissions to keep global warming below two degrees Celsius as the Paris accord promises, according to independent analyses.

Australian climate change denialists, including the Murdoch-media, continue to claim that the science is in dispute. An oft-quoted statistic is that 3% if climate scientists don’t think that human-caused global warming is real, often followed by a claim that the 97% who do think so are involved in some vast conspiracy or have vested interests (shares in solar panel companies perhaps?).  If 3% of climate scientists really think that anthropogenic global warming is not real, then perhaps there possibly are real uncertainties about the science.

So is the 97% figure an urban myth or real?  The figure actually comes from a 2013 article in Environmental Research Letters by Cook et al. titled “Quantifying the Consensus on Anthropogenic Global Warming in the Scientific Literature.” They reported that “Among abstracts expressing a position on AGW, 97.1% endorsed the consensus position that humans are causing global warming”. The 97 percent figure went viral and, not surprisingly, the qualifying phrase “expressing a position”—the fine print, —got dropped. Most of the remaining 3% did not express a position, very different from a climate-sceptical position. A more recent review of abstracts from 2013 and 2014 (the_consensus_on_anthropogenic_global_warming) found that of 24,210 abstracts of papers on climate change, only five explicitly rejected human role in global warming. As two of these papers were by the same author, the final figure for scientists who publish on global warming and reject a human causative role is 1 in 17,352 or 0.006%. This is probably as close to unanimity as humans are capable of.

Does this mean the projections quoted above are exact? Of course not. I know perhaps more than most that projections are uncertain, sometimes highly uncertain, and there are plenty of arguments within the literature about the details and impacts of global warming.  Whether scenario X or Y is likely optimistic or pessimistic, whether the sea level will rise more than half a metre by 2100 etc etc.  But none of this means there is not a very strong consensus on the big picture, the need to act now, and the likely implications of not acting strongly enough.

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New estimates of the causes of child death under age 5

WHO has just released the latest update on global causes of death for children under age 5 for years 2000-2017. These are available for download on the WHO website at and also in the Global Health Observatory at  A collaborating group of academic researchers led by Professor Bob Black from Johns Hopkins University carried out data analysis and modelling in collaboration with a number of WHO technical departments and myself.

Despite remarkable progress in the improvement of child survival globally, with a reduction in the annual number of child deaths from 10 million in 2000 to 5.4 million in 2017, this level of progress will need to accelerate to achieve the Sustainable Development Goal for child mortality in 2030. There remain many preventable child deaths in developing countries. The causes of the 5.4 million deaths of children under 5 are summarized in the following pie chart.

Global distribution of causes of child death under age 5, 2017


Almost half of deaths under 5 are now in the neonatal period (the first four weeks of life) where the causes of death are shaded yellow above and led by prematurity and birth asphyxia or trauma.  In the period 1-11 months the leading cause of death is acute respiratory infection (ARI) which is mostly pneumonia, followed by diarrheal diseases and injuries.

Reductions in mortality rates for pneumonia, diarrhoea, neonatal intrapartum-related events, malaria, and measles were responsible for 65% of the total reduction of under 5 deaths, pr just under 3 million of the 4.6 million deaths per year averted between 2000 and 2017 (see Figure below). Most of these causes relate mainly to the period 1-59 months after the neonatal period. The faster decline in these “post-neonatal” causes over the last 15 years has resulted in preterm birth complications now being the leading cause of under 5 deaths in 2017.


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Seven WHO staff named in world’s most highly cited list

Seven staff from the World Health Organization have been included in the 2018 Clarivate Analytics 2018 Highly Cited Researchers List. This list includes more than 4,000 leading researchers in 21 fields of the sciences and social sciences from around the world, including 17 Nobel laureates.

Now in its fifth edition, the list identifies influential researchers who have demonstrated significant influence on the research community through publication of multiple highly cited papers. The Web of Science is used as the basis for identifying researchers whose citation records position them in the top 1 percent by citations for their field over the last ten years.

Five of the WHO staff included in the list this year worked at the WHO Headquarters in Geneva:  Mercedes de Onis, Chris Dye, Colin Mathers, Susan Norris, and Gretchen Stevens. The other two, Freddie Bray and Jacques Ferlay work at the International Agency for Research on Cancer (IARC), WHO’s specialized cancer agency based in Lyon, France. Chris Dye, Gretchen Stevens and myself all left WHO earlier this year.

A new cross-field category was added this year to recognize researchers with substantial influence in several fields but who do not have enough highly cited papers in any one field to be chosen. Two of the WHO staff included this year were named in the cross-field category: Gretchen Stevens and Chris Dye.

In my work on global health statistics and burden of disease, I have collaborated widely with academics across the world, and also worked with many of them on WHO expert committees. Twenty-five of these academic collaborators are also included in the 2018 list of the world’s highly cited researchers, including leading researchers from Harvard University, University of Edinburgh, Imperial College London, the London School of Hygiene and Tropical Medicine, the Universities of NSW and Melbourne, the University of Toronto, and the University of Washington.

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Back in 2006, I published a paper in PLoS Medicine with detailed projections of deaths by age, sex and cause for all regions of the world, from year 2002 to 2030 (  That paper has proved very popular, with over 9000 citations to date.  I’ve updated these projections to most recent WHO baseline estimates several times, and following the release of the latest update of causes of death for year 2016 by WHO earlier this year (, I have done another update, extending the projections for the first time beyond 2030 to 2060.

This has now been released by WHO on its website at where regional and global projections can be downloaded in spreadsheet form, along with a methods note. Apart from synchronising the new projections with the 2016 cause of death estimates, the cause-specific trends in the near term are synchronized with estimated recent trends over the last 10 to 15 years. In the longer term, broad trends are largely driven by projection equations which model the epidemiological transition from infectious to non-communicable diseases in terms of projections of average income per capita, average years of education, time, and for some causes also projections of smoking impact.

In the original projections, separate projection models were developed for HIV/AIDS, tuberculosis, lung cancer, diabetes mellitus and chronic respiratory diseases.  These models were revised and updated for this latest update. Additional special projection models were also been developed for malaria, maternal deaths, road injury, homicide, natural disasters and war and conflict.

At the global level, age-standardized death rates for most important causes are falling with time, faster in most cases for infectious, maternal and perinatal causes than for non-communicable diseases (see figures below). The main exceptions are for diabetes, breast cancer and road injuries. The specific projection model for diabetes is based on projections of the prevalence of overweight and obesity and that for road injury is based on projections of vehicles per capita with continued economic development.

IHD = Ischaemic heart disease, COPD = Chronic Obstructive Pulmonary Disease,
ARI = Acute respiratory infection (mainly pneumonia), TB = tuberculosis

However, for many of these causes, the total projected deaths are rising with time because of population growth and ageing. Only the relatively fast declining infectious, maternal and perinatal causes are likely to also have declining total numbers of deaths (see the following two figures).

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Are countries on track to meet the global targets for noncommunicable diseases?

More than half of all countries are predicted to fail to reach the UN target to reduce premature deaths from cancers, cardiovascular disease, chronic respiratory disease, and diabetes by 2030, according to a new analysis published by the NCD Countdown 2030 collaborators in The Lancet ahead of the third UN High-Level Meeting on NCDs commencing on 27 September 2018. WHO is a member of the Countdown 2030 and the paper makes use of the most recent WHO estimates for causes of death released by my Unit earlier this year.

Cancers, cardiovascular diseases, chronic respiratory diseases, and diabetes were responsible for 12.5 million deaths among people aged 30-70 years worldwide in 2016. The following figure from the paper shows the of dying between ages 30 and 70 from these four non-communicable disease groups (referred to below as NCD4) for men and women.

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Noncommunicable disease mortality in tropical countries

The recent WHO update of causes of death for 186 countries in 2016 ( has been used as the basis for an assessment of the importance of non-communicable diseases (NCDs) in tropical countries. The paper “Acting on non-communicable diseases in low- and middle-income tropical countries” was published last week in Nature journal (Ezzati, Pearson-Stuttard, Bennett & Mathers, Nature The paper showed that most NCDs cause more deaths at every age in low- and middle-income tropical countries than in high-income Western countries.

The following graph from the paper compares NCD mortality in low- and middle-income tropical countries with that in high-income Western countries. The map (a) shows the share of deaths from NCDs, and map (b) shows the age-standardized death rates from NCDs.  The latter provides a standard measure of the risk of death from NCDs, which removes the effect of different population age structures.  It is clear that NCD mortality risks are higher in most tropical low- and middle-income countries than high income countries.  In contrast, the NCD share of deaths is higher in high income countries, because infectious disease death rates are much lower.

The paper goes on to examine the causes of NCDs in low- and middle-income countries, which  include poor nutrition and living environment, infections, insufficient taxation and regulation of tobacco and alcohol, and under-resourced and inaccessible healthcare. The paper also identifies a comprehensive set of actions across health, social, economic and environmental sectors that could confront NCDs in low- and middle-income tropical countries and reduce global health inequalities.

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Latest information on the state of the world’s health released by WHO

In mid-May, WHO released World Health Statistics 2018: Monitoring health for the SDGs  (WHS2018). This WHO flagship publication compiles data from the organization’s 194 Member States on 36 health-related Sustainable Development Goals (SDG) indicators, providing a snapshot of both gains and threats to the health of the world’s people. While the quality of health data has improved significantly in recent years, many countries still do not routinely collect high-quality data to monitor more than 50 health-related SDG indicators. Nine of the SDG health indicators reported in the WHS2018 are mortality indicators drawn from the latest update of the WHO Global Health Estimates released in April this year.

This update of estimates of death by cause, age and sex for years 2000 to 2016 for 187 countries and for 236 causes and cause groups is available at  Finalizing this update was a major focus of my work during my last months at WHO before retirement, and indeed, I continued to do some work after retirement to finalize numbers and documentation. So the 2018 World Health Statistics will be the last to which I have made substantial contributions. I have to recognize the huge efforts by my former team to produce and publish this report, in particular Annet Mahanani who was the overall project manager and editor, and Gretchen Stevens who played an important role both in the update of the Global Health Estimates and in the preparation of material and text for the WHS2018.

Since 2016 the World Health Statistics series has served as WHO’s annual report on the health-related Sustainable Development Goals (SDGs) and the 2018 report includes a section summarizing the current status of the health SDGs.

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