Christian Azar - Academia.edu (original) (raw)

Papers by Christian Azar

Biomass & Bioenergy, Nov 1, 2007

Earth’s Future, Jul 1, 2021

The Energy Journal, Sep 1, 2006

Climatic Change, Aug 18, 2011

Nature Climate Change, Mar 31, 2021

Research Square (Research Square), Apr 4, 2022

Frontiers in climate, Dec 7, 2021

The text in this book presents various system aspects on materials ows in society and nature and ... more The text in this book presents various system aspects on materials ows in society and nature and then mainly from a natural sciences and technical point of view. It is aiming at giving an overview of important material ows in society and in nature and their interactions in a sustainability perspective and the text is therefore of a more principal character. More examples and applications in specific sectors of society can be found in the other books of this series. Unfortunately, the examples and data presented in this book are exclusively from western countries. The documented and available studies on materials ows in the society and their connections to the environmental and resource problems are to an overwhelming majority describing western societies and this book has drawn from these studies.

Nature Sustainability, 2019

Climatic Change, May 1, 2022

npj Climate and Atmospheric Science, 2022

As researchers who have published over recent years on the issue of comparing the climate effects... more As researchers who have published over recent years on the issue of comparing the climate effects of different greenhouse gases, we would like to highlight a simple innovation that would enhance the transparency of stocktakes of progress towards achieving any multi-decade-timescale global temperature goal. In addition to specifying targets for total CO 2-equivalent emissions of all greenhouse gases, governments and corporations could also indicate the separate contribution to these totals from greenhouse gases with lifetimes around 100 years or longer, notably CO 2 and nitrous oxide, and the contribution from Short-Lived Climate Forcers (SLCFs), notably methane and some hydrofluorocarbons. This separate indication would support an objective assessment of the implications of aggregated emission targets for global temperature, in alignment with the UNFCCC Parties' Decision (4/ CMA.1) 1 to provide "information necessary for clarity, transparency and understanding" in nationally determined contributions (NDCs) and long-term low-emission development strategies (LT-LEDSs). While differences remain between us regarding how best to set fair yet ambitious targets for individual emitters 2-5 , including how any additional information might be used, and the interpretation of the Paris Agreement, it is important to emphasise the high level of agreement on the underlying science of how different greenhouse gases affect global temperature. The 2018 IPCC Special Report on 1.5°C (SR1.5) 6 stated "Reaching and sustaining net-zero global anthropogenic CO 2 emissions and declining net non-CO 2 radiative forcing (Planetary energy imbalance resulting directly from human-induced changes.) would halt anthropogenic global warming on multi-decadal timescales (high confidence). The maximum temperature reached is then determined by cumulative net global anthropogenic CO 2 emissions up to the time of net zero CO 2 emissions (high confidence) and the level of non-CO 2 radiative forcing in the decades prior to the time that maximum temperatures are reached (medium confidence)". The IPCC 6th Assessment Report (AR6) 7 confirmed "limiting human-induced global warming to a specific level requires limiting cumulative CO 2 emissions, reaching at least net zero CO 2 emissions, along with strong reductions in other greenhouse gas emissions". Parties to the Paris Agreement agreed in Katowice in 2018 (Decision 18/CMA.1) 1 to report past emissions of individual gases separately and use 100-year Global Warming Potentials (GWP 100

Climatic Change, 2000

The economist's vocabulary is seductive. Statements about efficient or even optimal solutions cre... more The economist's vocabulary is seductive. Statements about efficient or even optimal solutions create the impression that economics is a tool that can be used to provide policy makers with value neutral advice on what to do. In the case of climate change, we have by now become used to economists claiming to have found the optimal level of CO 2 emissions. Similar statements are common also in the context of other environmental problems. I have even witnessed a Canadian economics professor claiming that 'research suggests that there are too many forests in tropical countries' during his plenary speech at a conference on bioenergy. According to Hume, it is impossible to 'derive an ought from an is'. Although formulated two centuries ago, this is still a valuable reminder for students, researchers, policy makers and the general public. In order to derive an ought, e.g., the level of emission reduction that we should aim for, value judgements are necessary. This is important since the relevance for public policy of statements about economic optimality depends crucially upon the acceptability of the underlying value judgements. Unfortunately, in economic models of climate change, these value laden issues are often concealed in a seemingly value neutral language. This leaves policy makers with the impression that what the economist finds as optimal is also optimal in an objective, scientific or value neutral sense. In economic optimization models of climate change, there are several value laden assumptions, e.g., the value of statistical lives in rich and poor countries, the value of the future, the value of species and nature in general, as well as how to deal with low probability high impact events. These and other issues have been discussed in several publications over the past years, see e.g., Spash (1994), Schneider (1997), Azar (1998) or Chapman and Khanna (2000). The way these issues are dealt with is of critical importance for the outcome of benefit-cost analysis (BCA) of climate change. A small change in a sensitive, and value laden parameter may radically alter the outcome of a cost analysis (see e.g., Azar and Sterner, 1996, on discounting and valuation of damages in poor countries, and Roughgarden and Schneider, 1999, on uncertainty and valuation). Here, we will only consider one such issue: the decision making criterion employed in benefit-cost analysis, the so-called Hicks-Kaldor criterion.

WIREs Climate Change, 2011

Bioenergy can come to play a significant role in the global energy system and perhaps account for... more Bioenergy can come to play a significant role in the global energy system and perhaps account for one fifth of global energy supply in 50 years in response to ambitions to reduce carbon dioxide emissions. But bioenergy is complicated. There are both traditional and modern forms. In this article, I will exclusively look at modern forms, i.e., biomass for electricity, transport and heat, and process heat (not traditional forms used for cooking in developing countries). Furthermore, there are both ‘good’ and ‘bad’ kinds, expensive and inexpensive technologies, bioenergy systems that lead to massive carbon dioxide emissions and systems that are carbon neutral, and even ones that remove carbon dioxide from the atmosphere while delivering energy. There is concern that certain bioenergy forms will, in response to increasing carbon prices, become so attractive that food prices increase significantly, that poor people are evicted from their lands, and that rainforest and other sensitive ecos...

Earth System Dynamics Discussions, 2012

Metrics for comparing greenhouse gases are analyzed, with a particular focus on the integrated te... more Metrics for comparing greenhouse gases are analyzed, with a particular focus on the integrated temperature change potential (IGTP) following a call from IPCC to investigate this metric. It is shown that the global warming potential (GWP) and IGTP are asymptotically equal when the time horizon approaches infinity when standard assumptions about a constant background atmosphere are used. The difference between IGTP and GWP is estimated for different greenhouse gases using an upwelling diffusion energy balance model with different assumptions on the climate sensitivity and the parameterization governing the rate of ocean heat uptake. It is found that GWP and IGTP differ by some 10 % for CH 4 (for a time horizon of less than 500 yr), and that the relative difference between GWP and IGTP is less for gases with a longer atmospheric life time. Further, it is found that the relative difference between IGTP and GWP increases with increasing rates of ocean heat uptake and increasing climate sensitivity since these changes increase the inertia of the climate system. Furthermore, it is shown that IGTP is equivalent to the sustained global temperature change potential (SGTP) under standard assumptions when estimating GWPs. We conclude that while it matters little for abatement policy whether IGTP, SGTP or GWP is used when making tradeoffs, it is more important to decide whether society should use a metric based on time integrated effects such as GWP, a "snapshot metric" as GTP, or metrics where both economics and physical considerations are taken into account. Of equal importance is the question of how to choose the time horizon, regardless of the chosen metric. For both these overall questions, value judgments are needed.