Executive Summary

Chapter 17 explores possible transformational pathways of the future global energy system with the overarching aim of assessing the technological feasibility as well as the economic implications of meeting a range of sustainability objectives simultaneously. As such, it aims at the integration across objectives, and thus goes beyond earlier assessments of the future energy system that have mostly focused on either specific topics or single objectives. Specifically, the chapter assesses technical measures, policies, and related costs and benefits for meeting the objectives that were identified in Chapters 2 to 6, including:

• providing almost universal access to affordable clean cooking and electricity for the poor;

• limiting air pollution and health damages from energy use;

• improving energy security throughout the world; and

• limiting climate change.

The assessment of future energy pathways in this chapter shows that it is technically possible to achieve improved energy access, air quality, and energy security simultaneously while avoiding dangerous climate change. In fact, a number of alternative combinations of resources, technologies, and policies are found capable of attaining these objectives. From a large ensemble of possible transformations, three distinct groups of pathways (GEA-Supply, GEA-Mix, and GEA-Efficiency) have been identified and analyzed. Within each group, one pathway has been selected as “illustrative” in order to represent alternative evolutions of the energy system toward sustainable development. The pathway groups, together with the illustrative cases, depict salient branching points for policy implementation and highlight different degrees of freedom and different routes to the sustainability objectives.

Executive summary

Nature of the problem

• Observations of atmospheric reactive nitrogen (Nr) deposition are severely restricted in spatial extent and type. The chain of processes leading to atmospheric deposition emissions, atmospheric dispersion, chemical transformation and eventual loss from the atmosphere is extremely complex and therefore currently, observations can only address part of this chain.

Approaches

• Modelling provides a way of estimating atmospheric transport and deposition of Nr at the European scale. A description of the different model types is provided.

• Current deposition estimates from models are compared with observations from European air chemistry monitoring networks.

• The main focus of the chapter is at the European scale; however, both local variability and and intercontinental Nr transfers are also addressed.

Key findings/state of knowledge

• Atmospheric deposition is a major input of Nr for European terrestrial and freshwater ecosystems as well as coastal sea areas.

• Models are key tools to integrate our understanding of atmospheric chemistry and transport, and are essential for estimating the spatial distribution of deposition, and to support the formulation of air pollution control strategies.

• Our knowledge of the reliability of models for deposition estimates is, however, limited, since we have so few observational constraints on many key parameters.

• Total Nr deposition estimates cannot be directly assessed because of a lack of measurements, especially of the Nr dry deposition component. Differences among European regional models can be significant, however, e.g. 30% in some areas, and substantially more than this for specific locations.

‘Prediction is very difficult, especially if it's about the future’ (Niels Bohr, Nobel laureate in Physics). For instance, forecasters in Victorian London foresaw their city knee-deep in horse manure, one of the most pertinent urban environmental problems in cities at that time. A hundred years later, this prediction has not materialized and the situation has changed drastically. While traffic itself is still considered a major cause of urban air pollution, the contribution from horses has entirely disappeared and motorized vehicles are now the major source of deteriorated air quality in most modern cities.

Given the failure of simple extrapolations of present trends into the future, what can we say about air pollution in the coming decades?

To begin with, we know that population will further increase in urban areas, and we know that all societies aim to further strengthen their economic wealth. For a long time, air pollution from anthropogenic (non-natural) activities has been considered an unavoidable concomitant of economic development. Over long historic periods, we have seen air pollution levels increasing together with economic growth. Countermeasures to control air pollution have often been considered too costly to put into effect without compromising economic wealth.

Following this logic, the envisaged continued growth in global population, together with the universal target of improving prosperity, would lead to drastically worsened air quality around the globe, especially in many developing countries.